ALBERT

Description: 〈b〉Dynamic changes in optical and chemical properties of tar ball aerosols by atmospheric photochemical aging〈/b〉〈br〉 Chunlin Li, Quanfu He, Julian Schade, Johannes Passig, Ralf Zimmermann, Daphne Meidan, Alexander Laskin, and Yinon Rudich〈br〉 Atmos. Chem. Phys., 19, 139-163, https://doi.org/10.5194/acp-19-139-2019, 2019〈br〉 〈p〉Following wood pyrolysis, tar ball aerosols were laboratory generated from wood tar separated into polar and nonpolar phases. Chemical information of fresh tar balls was obtained from a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and single-particle laser desorption/resonance enhanced multiphoton ionization mass spectrometry (SP-LD-REMPI-MS). Their continuous refractive index (RI) between 365 and 425 nm was retrieved using a broadband cavity enhanced spectroscopy (BBCES). Dynamic changes in the optical and chemical properties for the nonpolar tar ball aerosols in 〈span〉NO〈sub〉〈i〉x〈/i〉〈/sub〉〈/span〉-dependent photochemical process were investigated in an oxidation flow reactor (OFR). Distinct differences in the chemical composition of the fresh polar and nonpolar tar aerosols were identified. Nonpolar tar aerosols contain predominantly high-molecular weight unsubstituted and alkyl-substituted polycylic aromatic hydrocarbons (PAHs), while polar tar aerosols consist of a high number of oxidized aromatic substances (e.g., methoxy-phenols, benzenediol) with higher O : C ratios and carbon oxidation states. Fresh tar balls have light absorption characteristics similar to atmospheric brown carbon (BrC) aerosol with higher absorption efficiency towards the UV wavelengths. The average retrieved RI is 〈span〉1.661+0.020〈i〉i〈/i〉〈/span〉 and 〈span〉1.635+0.003〈i〉i〈/i〉〈/span〉 for the nonpolar and polar tar aerosols, respectively, with an absorption Ångström exponent (AAE) between 5.7 and 7.8 in the detected wavelength range. The RI fits a volume mixing rule for internally mixed nonpolar/polar tar balls. The RI of the tar ball aerosols decreased with increasing wavelength under photochemical oxidation. Photolysis by UV light (254 nm), without strong oxidants in the system, slightly decreased the RI and increased the oxidation state of the tar balls. Oxidation under varying OH exposure levels and in the absence of 〈span〉NO〈sub〉〈i〉x〈/i〉〈/sub〉〈/span〉 diminished the absorption (bleaching) and increased the O : C ratio of the tar balls. The photobleaching via OH radical initiated oxidation is mainly attributed to decomposition of chromophoric aromatics, nitrogen-containing organics, and high-molecular weight components in the aged particles. Photolysis of nitrous oxide (〈span〉N〈sub〉2〈/sub〉O〈/span〉) was used to simulate 〈span〉NO〈sub〉〈i〉x〈/i〉〈/sub〉〈/span〉-dependent photochemical aging of tar balls in the OFR. Under high-〈span〉NO〈sub〉〈i〉x〈/i〉〈/sub〉〈/span〉 conditions with similar OH exposure, photochemical aging led to the formation of organic nitrates, and increased both oxidation degree and light absorption for the aged tar ball aerosols. These observations suggest that secondary organic nitrate formation counteracts the bleaching by OH radical photooxidation to eventually regain some absorption of the aged tar ball aerosols. The atmospheric implication and climate effects from tar balls upon various oxidation processes are briefly discussed.〈/p〉

Description: 〈b〉A Double ITCZ Phenomenology of Wind Errors in the Equatorial Atlantic in Seasonal Forecasts with ECMWF Models〈/b〉〈br〉 Jonathan K. P. Shonk, Teferi D. Demissie, and Thomas Toniazzo〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1316,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Modern climate models are affected by systematic biases that harm their ability to produce reliable seasonal forecasts and climate projections. In this study, we investigate causes of biases in wind patterns over the tropical Atlantic during northern spring in three related models. We find that the wind biases are associated with an increase in excess rainfall and convergence in the tropical western Atlantic at the start of April, leading to the redirection of trade winds away from the equator.

Description: 〈b〉New particle formation in the marine atmosphere during seven cruise campaigns〈/b〉〈br〉 Yujiao Zhu, Kai Li, Yanjie Shen, Yang Gao, Xiaohuan Liu, Yang Yu, Huiwang Gao, and Xiaohong Yao〈br〉 Atmos. Chem. Phys., 19, 89-113, https://doi.org/10.5194/acp-19-89-2019, 2019〈br〉 In this paper, we investigate new particle formation (NPF) events during seven cruises. NPF events were observed on 25 days and were most likely associated with the long-range transport of anthropogenic air pollutants. The relationship between the net generated amount of new particles and their apparent formation rate is established and explained in terms of the roles of different vapor precursors. The survival probability of new particles to CCN size is also discussed.

Description: 〈b〉Aircraft-based measurements of High Arctic springtime aerosol show evidence for vertically varying sources, transport and composition〈/b〉〈br〉 Megan D. Willis, Heiko Bozem, Daniel Kunkel, Alex K. Y. Lee, Hannes Schulz, Julia Burkart, Amir A. Aliabadi, Andreas B. Herber, W. Richard Leaitch, and Jonathan P. D. Abbatt〈br〉 Atmos. Chem. Phys., 19, 57-76, https://doi.org/10.5194/acp-19-57-2019, 2019〈br〉 The vertical distribution of Arctic aerosol is an important driver of its climate impacts. We present vertically resolved measurements of aerosol composition and properties made in the High Arctic during spring on an aircraft platform. We explore how aerosol properties are related to transport history and show evidence of vertical trends in aerosol sources, transport mechanisms and composition. These results will help us to better understand aerosol–climate interactions in the Arctic.

Description: 〈b〉Aerosol radiative effects with MACv2〈/b〉〈br〉 Stefan Kinne〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-949,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉onthly global maps for aerosol properties of the MACv2 climatology are applied in an off-line radiative transfer model to determine aerosol radiative effects. For details beyond global averages in most cases global maps are presented to visualize regional and seasonal details. Aside from the direct radiative (aerosol presence) effect, including those for aerosol components as extracted from MACv2 aerosol optics, also the major aerosol indirect radiative effect is covered. Hereby, the impact of smaller drops in water clouds due to added anthropogenic aerosol was simulated by applying a satellite retrieval based fit from locally associations between aerosol and drop concentrations over oceans. Present-day anthropogenic aerosols of MACv2 – on a global average basis – reduce the radiative net-fluxes at the top of the atmosphere (TOA) by −1.0 W/m〈sup〉2〈/sup〉 and at the surface by −2.1 W/m〈sup〉2〈/sup〉. Direct cooling contributions are only about half of indirect contributions (−.35 vs −.65) at TOA, but about twice at the surface (−1.45 vs −.65), as solar absorption of the direct effect warms the atmosphere by +1.1 W/m〈sup〉2〈/sup〉. Natural aerosols are on average less absorbing (for a relatively larger solar TOA cooling) and larger in size (now contributing with IR greenhouse warming). Thus, average TOA direct forcing efficiencies for total and anthropogenic aerosol happen to be similar: −11 W/m〈sup〉2〈/sup〉/AOD at all-sky and −24 W/m〈sup〉2〈/sup〉/AOD at clear-sky conditions. The present-day direct impact by all soot (BC) is globally averaged +0.55W/m〈sup〉2〈/sup〉 and at least half of it should be attributed to anthropogenic sources. Hereby any accuracy of anthropogenic impacts, not just for soot, suffers from the limited access to a pre-industrial reference. Anthropogenic uncertainty has a particular strong impact on aerosol indirect effects, which dominate the (TOA) forcing. Accounting for uncertainties in the anthropogenic definition, present-day aerosol forcing is estimated to stay within the −0.7 to −1.6 W/m〈sup〉2〈/sup〉 range, with a best estimate at −1 W/m〈sup〉2〈/sup〉. Calculations with model predicted temporal changes to anthropogenic AOD indicate that qualitatively the anthropogenic aerosol forcing has not changed much over the last decades and is not likely to increase over the next decades, despite strong regional shifts. These regional shifts explain most solar insolation (brightening or dimming) trends that have been observed by ground-based radiation data.〈/p〉

Description: 〈b〉Thermal structure of the mesopause region during the WADIS-2 rocket campaign〈/b〉〈br〉 Raimund Wörl, Boris Strelnikov, Timo P. Viehl, Josef Höffner, Pierre-Dominique Pautet, Michael J. Taylor, Yucheng Zhao, and Franz-Josef Lübken〈br〉 Atmos. Chem. Phys., 19, 77-88, https://doi.org/10.5194/acp-19-77-2019, 2019〈br〉 Simultaneous temperature measurements during the WADIS-2 rocket campaign are used to investigate the thermal structure of the mesopause region. Vertically and horizontally resolved in situ and remote measurements are in good agreement and show dominating long-term and large-scale waves with periods of 24 h and higher tidal harmonics. Only a few gravity waves with periods shorter than 6 h and small amplitudes are there.

Description: 〈b〉Classification of aerosol population type and cloud condensation nuclei properties in a coastal California littoral environment using an unsupervised cluster model〈/b〉〈br〉 Samuel A. Atwood, Sonia M. Kreidenweis, Paul J. DeMott, Markus D. Petters, Gavin C. Cornwell, Andrew C. Martin, and Kathryn A. Moore〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1297,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 This paper presents measurements of aerosol particles at a coastal location. The particles were classified into distinct aerosol types using both microphysical measurements and meteorological information, allowing rapid changes between the aerosol types to be reliably identified. These particles can alter cloud and precipitation processes, and inclusion of the differences between types can improve atmospheric models and remote sensing retrievals in littoral zones.

Description: 〈b〉Detection of Outflow of Formaldehyde and Glyoxal from the African continent to the Atlantic Ocean with a MAX-DOAS Instrument〈/b〉〈br〉 Lisa K. Behrens, Andreas Hilboll, Andreas Richter, Enno Peters, Leonardo M. A. Alvarado, Anna B. Kalisz Hedegaard, Folkard Wittrock, John P. Burrows, and Mihalis Vrekoussis〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1286,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 MAX-DOAS measurements were conducted on the research vessel Maria S. Merian during a cruise from the Azores to South Africa in October 2016. The measurements indicate enhanced levels of HCHO and CHOCHO over the remote Atlantic Ocean, which is unexpected due to their short lifetime. Precursors of these gases or gas-aerosol combinations might be transported. Model simulations indicate potential source regions over the African continent, probably related to biomass burning or biogenic emissions.

Description: 〈b〉Primary and secondary sources of ambient formaldehyde in the Yangtze River Delta based on OMPS observation〈/b〉〈br〉 Wenjing Su, Cheng Liu, Qihou Hu, Shaohua Zhao, Youwen Sun, Wei Wang, Yizhi Zhu, Jianguo Liu, and Jhoon Kim〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1192,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 For a better understanding of the pollution and atmospheric chemistry of HCHO, we evaluated its primary and secondary sources in the Yangtze River Delta based on HCHO column density from Ozone Mapping and Profiler Suite (OMPS) and combining with surface in-situ measurements. We found that secondary formation contributed most to ambient HCHO for a long time, but primary emission could be dominant in the winter. The usability of total HCHO as the proxy of VOCs reactivity depends on time scale.

Description: 〈b〉Insights into the O : C dependent mechanisms controlling the evaporation of α-pinene secondary organic aerosol particles〈/b〉〈br〉 Angela Buchholz, Andrew T. Lambe, Arttu Ylisirniö, Zijun Li, Olli-Pekka Tikkanen, Celia Faiola, Eetu Kari, Liqing Hao, Olli Luoma, Wei Huang, Claudia Mohr, Douglas R. Worsnop, Sergey A. Nizkorodov, Taina Yli-Juuti, Siegfried Schobesberger, and Annele Virtanen〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1305,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 We studied the evaporation of α-pinene secondary organic aerosol particles in clean air to derive their volatility from the observed size changes. We found that the particles became more resilient to evaporation with increased oxidative age, possibly increasing their lifetime in the atmosphere. Also, increased relative humidity increased the particle evaporation. Mass spectrometry measurements of the particles at different stages of evaporation revealed some water-induced composition changes.

Description: 〈b〉Analyses of temperature and precipitation in the Indian Jammu and Kashmir region for the 1980–2016 period: implications for remote influence and extreme events〈/b〉〈br〉 Sumira Nazir Zaz, Shakil Ahmad Romshoo, Ramkumar Thokuluwa Krishnamoorthy, and Yesubabu Viswanadhapalli〈br〉 Atmos. Chem. Phys., 19, 15-37, https://doi.org/10.5194/acp-19-15-2019, 2019〈br〉 This paper is of first of its kind for the Jammu and Kashmir (western Himalayas) region, India. It shows the clear relation between the upper tropospheric Rossby wave activity (potential vorticity at the 350 K potential temperature and 200 mb level surface pressure) and the surface weather parameters (e.g., precipitation) over a period of 3 decades during 1980–2016. This indicates that the climatic weather pattern over the Kashmir region is influenced mostly by global climate change processes.

Description: 〈b〉Large increases in N〈sub〉cn〈/sub〉 and N〈sub〉ccn〈/sub〉 together with a nucleation-modeparticle pool over the northwestern Pacific Ocean in the spring of 2014〈/b〉〈br〉 Juntao Wang, Yanjie Shen, Kai Li, Yang Gao, Huiwang Gao, and Xiaohong Yao〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1089,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 In this paper, we studied the spatiotemporal variability of N〈sub〉cn〈/sub〉 and particle number size distributions, as well as N〈sub〉ccn〈/sub〉 and CCN activities over the NWPO in the spring of 2014. Several new findings have been revealed and discussed, e.g., large increases of N〈sub〉cn〈/sub〉 and N〈sub〉ccn〈/sub〉, against historical data and small contributions of dust and BB aerosols to N〈sub〉cn〈/sub〉 and N〈sub〉ccn〈/sub〉 on the monthly time scale, etc. This work may help understand the influence of the current outflow from the Asian continent on the climate.

Description: 〈b〉On what scales can GOSAT flux inversions constrain anomalies in terrestrial ecosystems?〈/b〉〈br〉 Brendan Byrne, Dylan B. A. Jones, Kimberly Strong, Saroja M. Polavarapu, Anna B. Harper, David F. Baker, and Shamil Maksyutov〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-909,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Spatial and temporal variations in atmospheric CO〈sub〉2〈/sub〉 are driven by fluxes of CO〈sub〉2〈/sub〉 at Earth's surface. Therefore, measurements of variations in atmospheric CO〈sub〉2〈/sub〉 from satellites, such as the Greenhouse Gases Observing Satellite (GOSAT), inform the spatiotemporal variations in CO〈sub〉2〈/sub〉 fluxes at Earth's surface. In this study, we examine how well interannual variations in CO〈sub〉2〈/sub〉 surface fluxes can be estimated from GOSAT measurements. We show estimated CO〈sub〉2〈/sub〉 anomalies are correlated with temperature anomalies.

Description: 〈b〉The importance of crystalline phases in ice nucleation by volcanic ash〈/b〉〈br〉 Elena C. Maters, Donald B. Dingwell, Corrado Cimarelli, Dirk Müller, Thomas F. Whale, and Benjamin J. Murray〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1326,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 This experimental study investigates the influence of volcanic ash chemical composition, crystallinity, and mineralogy on its ability to promote freezing of supercooled water. The results indicate that crystals in ash play a key role in this process, and suggest that alkali and plagioclase feldspars in ash may be highly ice-active. These findings contribute to improving understanding of the potential of ash emissions from different explosive eruptions to impact ice formation in the atmosphere.

Description: 〈b〉Local and regional contributions to fine particulate matter in the 18 cities of Sichuan Basin, southwestern China〈/b〉〈br〉 Xue Qiao, Hao Guo, Ya Tang, Pengfei Wang, Wenye Deng, Xing Zhao, Jianlin Hu, Qi Ying, and Hongliang Zhang〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1214,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 A source-oriented version of the CMAQ model was used to quantify contributions from nine regions to PM〈sub〉2.5〈/sub〉 and its components in the 18 cities within the Sichuan Basin. Non-local emissions contribute to 39~66 % and 25~52 % to the citywide average PM〈sub〉2.5〈/sub〉 concentrations of 45~126 and 14~31 μg m〈sup〉−3〈/sup〉 in the winter and summer, respectively. This study demonstrates the importance of joint emission control efforts among cities within the SCB and neighbor regions to the east.

Description: 〈b〉The significant contribution of HONO to secondary pollutants during a severe winter pollution event in southern China〈/b〉〈br〉 Xiao Fu, Tao Wang, Li Zhang, Qinyi Li, Zhe Wang, Men Xia, Hui Yun, Weihao Wang, Chuan Yu, Dingli Yue, Yan Zhou, Junyun Zheng, and Rui Han〈br〉 Atmos. Chem. Phys., 19, 1-14, https://doi.org/10.5194/acp-19-1-2019, 2019〈br〉 This study has identified the major contributors to the observed high HONO levels during a severe winter pollution episode and highlighted the importance of HONO chemistry in the combined photochemical and haze pollution in a subtropical region. It also highlighted the critical need to include and update HONO sources in regional air quality models in order to predict ozone and other secondary pollutants better during heavy pollution events in southern China and similar regions.

Description: 〈b〉On the fine vertical structure of the low troposphere over the coastal margins of East Antarctica〈/b〉〈br〉 Étienne Vignon, Olivier Traullé, and Alexis Berne〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1197,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 The sea-level rise associated to climate change will depend on how much the Antarctic ice sheet gain – viz precipitation – or loose mass. The precipitation simulation by climate models used for projections depends on the representation of the atmospheric circulation over and around Antarctica. Using daily measurements from balloon soundings at nine stations, this study characterizes the structure of the atmosphere over the Antarctic coast and assess its representation in a climate model.

Description: 〈b〉Is water vapor a key player of the wintertime haze in North China Plain?〈/b〉〈br〉 Jiarui Wu, Naifang Bei, Bo Hu, Suixin Liu, Meng Zhou, Qiyuan Wang, Xia Li, Lang Liu, Tian Feng, Zirui Liu, Yichen Wang, Junji Cao, Xuexi Tie, Jun Wang, Luisa T. Molina, and Guohui Li〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1289,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 The near-surface PM〈sub〉2.5〈/sub〉 contribution of the ALW total effect is 17.5 % in NCP, indicating that ALW plays an important role in the PM〈sub〉2.5〈/sub〉 formation during the wintertime haze pollution. Moreover, the ALW-HET overwhelmingly dominates the PM〈sub〉2.5〈/sub〉 enhancement due to the ALW. The ALW does not consistently enhance near-surface [PM〈sub〉2.5〈/sub〉] with increasing RH. When the RH exceeds 80 %, the contribution of the ALW commences to decrease caused by the high occurrence frequencies of precipitation.

Description: 〈b〉Towards an advanced observation system for the marine Arctic in the framework of the Pan-Eurasian Experiment (PEEX)〈/b〉〈br〉 Timo Vihma, Petteri Uotila, Stein Sandven, Dmitry Pozdnyakov, Alexander Makshtas, Alexander Pelyasov, Roberta Pirazzini, Finn Danielsen, Sergey Chalov, Hanna K. Lappalainen, Vladimir Ivanov, Ivan Frolov, Anna Albin, Bin Cheng, Sergey Dobrolyubov, Viktor Arkhipkin, Stanislav Myslenkov, Tuukka Petäjä, and Markku Kulmala〈br〉 Atmos. Chem. Phys., 19, 1941-1970, https://doi.org/10.5194/acp-19-1941-2019, 2019〈br〉 The Arctic marine climate system, ecosystems, and socio-economic systems are changing rapidly. This calls for the establishment of a marine Arctic component of the Pan-Eurasian Experiment (MA-PEEX), for which we present a plan. The program will promote international collaboration; sustainable marine meteorological, sea ice, and oceanographic observations; advanced data management; and multidisciplinary research on the marine Arctic and its interaction with the Eurasian continent.

Description: 〈b〉MICS-Asia III: Multi-model comparison and evaluation of aerosol over East Asia〈/b〉〈br〉 Lei Chen, Yi Gao, Meigen Zhang, Joshua S. Fu, Jia Zhu, Hong Liao, Jialin Li, Kan Huang, Baozhu Ge, Xuemei Wang, Yun Fat LAM, Chuan Yao Lin, Syuichi Itahashi, Tatsuya Nagashima, Mizuo Kajino, Kazuyo Yamaji, Zifa Wang, and Jun-ichi Kurokawa〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1346,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Simulated aerosol concentrations from 14 CTMs within the framework of MICS–Asia III are detailedly evaluated with an extensive set of measurements in East Asia. Similarities and differences among model performances are also analyzed. Although more considerable capacities for reproducing the aerosol concentrations and their variations are shown in current CTMs than those in MICS–Asia II, more efforts are needed to reduce diversities of simulated aerosol concentrations among air quality models.

Description: 〈b〉Contributions of different anthropogenic volatile organic compound sources to ozone formation at a receptor site in the Pearl River Delta region and its policy implications〈/b〉〈br〉 Zhuoran He, Xuemei Wang, Zhenhao Ling, Jun Zhao, Hai Guo, Min Shao, and Zhe Wang〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1293,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 In this study, source apportionment of volatile organic compounds (VOCs) and their contributions to photochemical O〈sub〉3〈/sub〉 formation was analyzed by the Positive Matrix Factorization model and an observation-based model for data collected at a receptor site in the Pearl River Delta (PRD) region. Furthermore, the policies for controlling VOC were brief reviewed. The findings could provide quantitative information on devising appropriate measures on the VOCs, NOx, and O〈sub〉3〈/sub〉 pollution in PRD.

Description: 〈b〉Characterisation and source identification of biofluorescent aerosol emissions over winter and summer periods in the United Kingdom〈/b〉〈br〉 Elizabeth Forde, Martin Gallagher, Virginia Foot, Roland Sarda-Esteve, Ian Crawford, Paul Kaye, Warren Stanley, and David Topping〈br〉 Atmos. Chem. Phys., 19, 1665-1684, https://doi.org/10.5194/acp-19-1665-2019, 2019〈br〉 The abundance and diversity of airborne biological particles in different environments remains poorly constrained. Measurements of such particles were conducted at four sites in the United Kingdom, using real-time fluorescence instrumentation. Using local land cover types, sources of suspected particle types were identified and compared. Most sites exhibited a wet-discharged fungal spore dominance, with the exception of one site, which was inferred to be influenced by a local dairy farm.

Description: 〈b〉Evidence for a major missing source in the global chloromethane budget from stable carbon isotopes〈/b〉〈br〉 Enno Bahlmann, Frank Keppler, Julian Wittmer, Markus Greule, Heinz Friedrich Schöler, Richard Seifert, and Cornelius Zetzsch〈br〉 Atmos. Chem. Phys., 19, 1703-1719, https://doi.org/10.5194/acp-19-1703-2019, 2019〈br〉 Chloromethane is the most important natural carrier of chlorine to the stratosphere. From a newly determined carbon isotope effect of −11.2 ‰ for the tropospheric loss of CH〈sub〉3〈/sub〉Cl we derive a tropical rainforest CH〈sub〉3〈/sub〉Cl source of 670 ± 200 Gg a〈sup〉−1〈/sup〉, 60 % smaller than previous estimates. A revision of previous bottom-up estimates using above-ground biomass instead of rainforest area strongly supports this lower estimate. Our results suggest a large unknown tropical value of 1530 ± 200 Gg a〈sup〉−1〈/sup〉.

Description: 〈b〉New particle formation in the active volcanic plume of the Piton de la Fournaise: specific features from a long-term dataset〈/b〉〈br〉 Clémence Rose, Brice Foucart, David Picard, Aurélie Colomb, Jean-Marc Metzger, Pierre Tulet, and Karine Sellegri〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-100,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 New particle formation (NPF) is a significant climate-relevant source of aerosols in the atmosphere. We show that during the eruptive period of the Piton de la Fournaise in 2015, NPF was favoured compared to regular days. Using the largest data set ever reported in volcanic plume conditions, we quantify the emission rates of particles over a broad size range and provide a new statistically robust parameterization to take into account this important source of atmospheric particles in models.

Description: 〈b〉Turbulent enhancement of radar reflectivity factor for polydisperse cloud droplets〈/b〉〈br〉 Keigo Matsuda and Ryo Onishi〈br〉 Atmos. Chem. Phys., 19, 1785-1799, https://doi.org/10.5194/acp-19-1785-2019, 2019〈br〉 This paper presents a parameterization to predict the influence of microscale turbulent clustering of cloud droplets on the radar reflectivity factor, based on a direct numerical simulation (DNS) of turbulence. The proposed parameterization takes account of the turbulent clustering structure of droplets with arbitrary size distributions. This paper also discusses quantitative influences on realistic radar observations, applying the parameterization to high-resolution cloud-simulation data.

Description: 〈b〉Kinetic mass-transfer calculation of water isotope fractionation due to cloud microphysics in a regional meteorological model〈/b〉〈br〉 I-Chun Tsai, Wan-Yu Chen, Jen-Ping Chen, and Mao-Chang Liang〈br〉 Atmos. Chem. Phys., 19, 1753-1766, https://doi.org/10.5194/acp-19-1753-2019, 2019〈br〉 In conventional models, isotope exchange between liquid and gas phases is usually assumed to be in equilibrium, and the highly kinetic phase transformation processes inferred in clouds are yet to be fully investigated. We show that different factors controlling isotopic composition, including water vapor sources, atmospheric transport, phase transition pathways of water in clouds, and kinetic-versus-equilibrium mass transfer, contributed significantly to the variations in isotope composition.

Description: 〈b〉Biomass-burning smoke heights over the Amazon observed from space〈/b〉〈br〉 Laura Gonzalez-Alonso, Maria Val Martin, and Ralph A. Kahn〈br〉 Atmos. Chem. Phys., 19, 1685-1702, https://doi.org/10.5194/acp-19-1685-2019, 2019〈br〉 The vertical distribution of fire smoke and factors that control its rise had not yet been quantified across the Amazon. We developed a satellite-based long record of smoke plume heights. We find that smoke heights are driven by many factors: vegetation, seasonality, time of day, fire intensity, and atmospheric and drought conditions. Also, drought increases fire pollution, with implications for air quality. Policies to control fires may be crucial in the future as more droughts are projected.

Description: 〈b〉Retrieving the age of air spectrum from tracers: principle and method〈/b〉〈br〉 Aurélien Podglajen and Felix Ploeger〈br〉 Atmos. Chem. Phys., 19, 1767-1783, https://doi.org/10.5194/acp-19-1767-2019, 2019〈br〉 The age spectrum (distribution of transit times) provides a compact description of transport from the surface to a given point in the atmosphere. It also determines the surface-emitted tracer content of an air parcel. We propose a method to invert this relation in order to retrieve age spectra from tracer concentrations and demonstrate its feasibility in idealized and model setups. Applied to observations, the approach might help to better constrain atmospheric transport timescales.

Description: 〈b〉Impact of a nitrogen emission control area (NECA) on the future air quality and nitrogen deposition to seawater in the Baltic Sea region〈/b〉〈br〉 Matthias Karl, Johannes Bieser, Beate Geyer, Volker Matthias, Jukka-Pekka Jalkanen, Lasse Johansson, and Erik Fridell〈br〉 Atmos. Chem. Phys., 19, 1721-1752, https://doi.org/10.5194/acp-19-1721-2019, 2019〈br〉 Air emissions of nitrogen oxides from ship traffic in the Baltic Sea are a health concern in coastal areas of the Baltic Sea region. We find that the introduction of the nitrogen emission control area (NECA) is critical for reducing ship emissions of nitrogen oxides to levels that are low enough to sustainably dampen ozone production. The decline of the ship-related nitrogen deposition to the Baltic Sea between 2012 and 2040 varies between 46 % and 78 % in different regulation scenarios.

Description: 〈b〉Physical properties of secondary photochemical aerosol from OH oxidation of a cyclic siloxane〈/b〉〈br〉 Nathan J. Janechek, Rachel F. Marek, Nathan Bryngelson, Ashish Singh, Robert L. Bullard, William H. Brune, and Charles O. Stanier〈br〉 Atmos. Chem. Phys., 19, 1649-1664, https://doi.org/10.5194/acp-19-1649-2019, 2019〈br〉 Cyclic volatile methyl siloxanes (cVMSs) are widely used chemicals in personal care products which can undergo oxidation to generate secondary organic aerosol. In this work, cVMS oxidation aerosols were generated using a photochemical chamber and the physical properties characterized. The aerosol yield, volatility, hygroscopicity, morphology, elemental composition, and proposed parameters for treatment as secondary organic aerosol in atmospheric models are provided.

Description: 〈b〉Local air pollution from oil rig emissions observed during the airborne DACCIWA campaign〈/b〉〈br〉 Vanessa Brocchi, Gisèle Krysztofiak, Adrien Deroubaix, Greta Stratmann, Daniel Sauer, Hans Schlager, Konrad Deetz, Guillaume Dayma, Claude Robert, Stéphane Chevrier, and Valéry Catoire〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-27,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 This study reports the first flaring in-situ measurements in southern West Africa. According to the measurements, oil rig flaring plumes in Ghana lead to increases in NO〈sub〉2〈/sub〉 and aerosols but not always in CO and not in SO〈sub〉2〈/sub〉. Flaring measurements can be reproduced using FLEXPART model, adjusting both the emission flux and the injection height. The DACCIWA satellite flaring inventory provides a reasonable estimate of flaring emission.

Description: 〈b〉Atmospheric band fitting coefficients derived from a self-consistent rocket-borne experiment〈/b〉〈br〉 Mykhaylo Grygalashvyly, Martin Eberhart, Jonas Hedin, Boris Strelnikov, Franz-Josef Lübken, Markus Rapp, Stefan Löhle, Stefanos Fasoulas, Mikhail Khaplanov, Jörg Gumbel, and Ekaterina Vorobeva〈br〉 Atmos. Chem. Phys., 19, 1207-1220, https://doi.org/10.5194/acp-19-1207-2019, 2019〈br〉 Based on rocket-borne true common volume observations of atomic oxygen, atmospheric band emission (762 nm), and background atmosphere density and temperature, one-step, two-step, and combined mechanisms of O〈sub〉2〈/sub〉(〈i〉b〈/i〉〈sup〉1〈/sup〉Σg〈sup〉+〈/sup〉) formation were analyzed. We found new coefficients for the fit function based on self-consistent temperature, atomic oxygen, and volume emission observations. This can be used for atmospheric band volume emission modeling or the estimation of atomic oxygen by known volume emission.

Description: 〈b〉Effects of organic coating on the nitrate formation by suppressing the N〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 heterogeneous hydrolysis: A case study during wintertime in Beijing-Tianjin-Hebei (BTH)〈/b〉〈br〉 Lang Liu, Jiarui Wu, Suixin Liu, Xia Li, Jiamao Zhou, Tian Feng, Yang Qian, Junji Cao, Xuexi Tie, and Guohui Li〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-25,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 〈p〉Although stringent emission mitigation strategies have been carried out since 2013 in Beijing-Tianjin-Hebei (BTH), China, heavy haze with high levels of fine particulate matters (PM〈sub〉2.5〈/sub〉) still frequently engulfs the region during wintertime and the nitrate contribution to PM〈sub〉2.5〈/sub〉 mass has progressively increased. The N〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 heterogeneous hydrolysis is referred to as the most important pathway of the nitrate formation at nighttime. In the present study, the WRF-CHEM model is applied to simulate a heavy haze episode from 10 to 27 February 2014 in BTH to evaluate the contribution of the N〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 heterogeneous hydrolysis and the effect of organic coating to the nitrate formation. The model generally performs reasonably well in simulating meteorological parameters, air pollutants and aerosol species against observations in BTH. The N〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 heterogeneous hydrolysis with all the secondary organic aerosol assumed to be involved in coating considerably improves the nitrate simulations compared to the measurements in Beijing. On average, organic coating decreases nitrate concentrations by 8.4 % in BTH during the episode, and the N〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 heterogeneous hydrolysis with organic coating contributes about 30.1 % of nitrate concentrations. Additionally, the reaction also plays a considerable role in the heavy haze formation, with a PM〈sub〉2.5〈/sub〉 contribution of about 11.6 % in BTH. Sensitivity studies also reveal that future studies need to be conducted to predict the organic aerosol hygroscopicity for accurately representing the organic coating effect on the N〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 heterogeneous hydrolysis.〈/p〉

Description: 〈b〉Cloud feedbacks in extratropical cyclones: insight from long-term satellite data and high-resolution global simulations〈/b〉〈br〉 Daniel T. McCoy, Paul R. Field, Gregory S. Elsaesser, Alejandro Bodas-Salcedo, Brian H. Kahn, Mark D. Zelinka, Chihiro Kodama, Thorsten Mauritsen, Benoit Vanniere, Malcolm Roberts, Pier L. Vidale, David Saint-Martin, Aurore Voldoire, Rein Haarsma, Adrian Hill, Ben Shipway, and Jonathan Wilkinson〈br〉 Atmos. Chem. Phys., 19, 1147-1172, https://doi.org/10.5194/acp-19-1147-2019, 2019〈br〉 The largest single source of uncertainty in the climate sensitivity predicted by global climate models is how much low-altitude clouds change as the climate warms. Models predict that the amount of liquid within and the brightness of low-altitude clouds increase in the extratropics with warming. We show that increased fluxes of moisture into extratropical storms in the midlatitudes explain the majority of the observed trend and the modeled increase in liquid water within these storms.

Description: 〈b〉Long-range-transported Canadian smoke plumes in the lower stratosphere over northern France〈/b〉〈br〉 Qiaoyun Hu, Philippe Goloub, Igor Veselovskii, Juan-Antonio Bravo-Aranda, Ioana Elisabeta Popovici, Thierry Podvin, Martial Haeffelin, Anton Lopatin, Oleg Dubovik, Christophe Pietras, Xin Huang, Benjamin Torres, and Cheng Chen〈br〉 Atmos. Chem. Phys., 19, 1173-1193, https://doi.org/10.5194/acp-19-1173-2019, 2019〈br〉 Smoke plumes generated in Canadian fire activities were elevated to the lower stratosphere and transported from North America to Europe. The smoke plumes were observed by three lidar systems in northern France. This study provides a comprehensive characterization for aged smoke aerosols at high altitude using lidar observations. It presents that fire activities on the Earth's surface can be an important contributor of stratospheric aerosols and impact the Earth's radiation budget.

Description: 〈b〉In-cloud formation of secondary species in iron-containing particles〈/b〉〈br〉 Qinhao Lin, Xinhui Bi, Guohua Zhang, Yuxiang Yang, Long Peng, Xiufeng Lian, Yuzhen Fu, Mei Li, Duohong Chen, Mark Miller, Ji Ou, Mingjin Tang, Xinming Wang, Ping'an Peng, Guoying Sheng, and Zhen Zhou〈br〉 Atmos. Chem. Phys., 19, 1195-1206, https://doi.org/10.5194/acp-19-1195-2019, 2019〈br〉 〈p〉The increase in secondary species through cloud processing potentially increases aerosol iron (Fe) bioavailability. In this study, a ground-based counterflow virtual impactor coupled with a real-time single-particle aerosol mass spectrometer was used to characterize the formation of secondary species in Fe-containing cloud residues (dried cloud droplets) at a mountain site in southern China for nearly 1 month during the autumn of 2016. Fe-rich, Fe-dust, Fe-elemental carbon (Fe-EC), and Fe-vanadium (Fe-V) cloud residual types were obtained in this study. The Fe-rich particles, related to combustion sources, contributed 84 % (by number) to the Fe-containing cloud residues, and the Fe-dust particles represented 12 %. The remaining 4 % consisted of the Fe-EC and Fe-V particles. It was found that above 90 % (by number) of Fe-containing particles had already contained sulfate before cloud events, leading to no distinct change in number fraction (NF) of sulfate during cloud events. Cloud processing contributed to the enhanced NFs of nitrate, chloride, and oxalate in the Fe-containing cloud residues. However, the in-cloud formation of nitrate and chloride in the Fe-rich type was less obvious relative to the Fe-dust type. The increased NF of oxalate in the Fe-rich cloud residues was produced via aqueous oxidation of oxalate precursors (e.g., glyoxylate). Moreover, Fe-driven Fenton reactions likely increase the formation rate of aqueous-phase OH, improving the conversion of the precursors to oxalate in the Fe-rich cloud residues. During daytime, the decreased NF of oxalate in the Fe-rich cloud residues was supposed to be due to the photolysis of Fe-oxalate complexes. This work emphasizes the role of combustion Fe sources in participating in cloud processing and has important implications for evaluating Fe bioavailability from combustion sources during cloud processing.〈/p〉

Description: 〈b〉Long-term simulation of the boundary layer flow over the double-ridge site during the Perdigão 2017 field campaign〈/b〉〈br〉 Johannes Wagner, Thomas Gerz, Norman Wildmann, and Kira Gramitzky〈br〉 Atmos. Chem. Phys., 19, 1129-1146, https://doi.org/10.5194/acp-19-1129-2019, 2019〈br〉 Long-term WRF-LES simulations were performed with a horizontal resolution of 200 m for a period of 49 days during the Perdigão campaign. Simulation results were used to characterize the meteorological conditions and to analyse characteristic flow patterns. It could be shown that thermally driven flows including low-level jets frequently occurred during the observation period. Model results were in very good agreement with observations in spite of the long simulation time.

Description: 〈b〉New particle formation from sulfuric acid and ammonia: nucleation and growth model based on thermodynamics derived from CLOUD measurements for a wide range of conditions〈/b〉〈br〉 Andreas Kürten〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1323,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 New particle formation and growth are important processes affecting climate and air quality. A significant fraction of the newly-formed particles is thought to originate from sulfuric acid, water and ammonia. The present study introduces a process model for the calculation of aerosol nucleation and growth rates for this chemical system. The thermodynamic parameters enabling these calculations are derived from laboratory (CLOUD chamber) measurements.

Description: 〈b〉Effects of turbulence structure and urbanization on the heavy haze pollution process〈/b〉〈br〉 Yan Ren, Hongsheng Zhang, Wei Wei, Bingui Wu, Xuhui Cai, and Yu Song〈br〉 Atmos. Chem. Phys., 19, 1041-1057, https://doi.org/10.5194/acp-19-1041-2019, 2019〈br〉 During the heavy pollution process, there are overestimations regarding the exchange between the atmosphere and surface since the normal calculation of turbulent fluxes includes the impact of sub-mesoscale motion. The intermittent turbulence intensity is closely related to the concentration of PM2.5. The intermittency is weaker over the complex surface condition than over the flat terrain, and urbanization reduces the degree of weakening in turbulent exchange during the heavy pollution process.

Description: 〈b〉Insight into the Composition of Organic Compounds (≥ C〈sub〉6〈/sub〉) in PM〈sub〉2.5〈/sub〉 in Wintertime in Beijing, China〈/b〉〈br〉 Ruihe Lyu, Zongbo Shi, Mohammed Salim Alam, Xuefang Wu, Di Liu, Tuan V. Vu, Christopher Stark, Pingqing Fu, Yinchang Feng, and Roy M. Harrison〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1273,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Severe pollution of the Beijing atmosphere is a frequent occurrence. The airborne particles which characterise the episodes of haze contain a wide range of chemical constituents but organic compounds make up a substantial proportion. In this study individual compounds have been analysed under both haze and non-haze conditions and the measurements are compared with samples collected in London where the air pollution climate and sources are very different.

Description: 〈b〉Photochemical impacts of haze pollution in an urban environment〈/b〉〈br〉 Michael Hollaway, Oliver Wild, Ting Yang, Yele Sun, Weiqi Xu, Conghui Xie, Lisa Whalley, Eloise Slater, Dwayne Heard, and Dantong Liu〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-29,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 This study, for the first time, uses combinations of aerosol and lidar data to drive an offline photolysis scheme. Absorbing species are shown to have the greatest impact on photolysis rate constants in the winter and scattering aerosol are shown to dominate responses in the summer. During haze episodes, aerosols are shown to produce a greater impact than cloud cover. The findings demonstrate the potential photochemical impacts of haze pollution in a highly polluted urban environment.

Description: 〈b〉Heterogeneous ice nucleation on dust particles sourced from nine deserts worldwide – Part 2: Deposition nucleation and condensation freezing〈/b〉〈br〉 Yvonne Boose, Philipp Baloh, Michael Plötze, Johannes Ofner, Hinrich Grothe, Berko Sierau, Ulrike Lohmann, and Zamin A. Kanji〈br〉 Atmos. Chem. Phys., 19, 1059-1076, https://doi.org/10.5194/acp-19-1059-2019, 2019〈br〉 The role non-mineral components play in the freezing behavior of atmospheric desert dust is not well known. In this study, we use chemical imaging methods to investigate this for airborne and surface-collected desert dust samples. We find that in most cases the ice nucleation behavior is determined by the dust mineralogical composition. However, volatile organic material can coat active sites and decrease the dust ice nucleation ability, while biological particles can significantly increase it.

Description: 〈b〉Estimation of ground-level particulate matter concentrations through the synergistic use of satellite observations and process-based models over South Korea〈/b〉〈br〉 Seohui Park, Minso Shin, Jungho Im, Chang-Keun Song, Myungje Choi, Jhoon Kim, Seungun Lee, Rokjin Park, Jiyoung Kim, Dong-Won Lee, and Sang-Kyun Kim〈br〉 Atmos. Chem. Phys., 19, 1097-1113, https://doi.org/10.5194/acp-19-1097-2019, 2019〈br〉 This study proposed machine-learning-based models to estimate ground-level particulate matter concentrations using satellite observations and numerical model-derived data. Aerosol optical depth was identified as the most significant for estimating ground-level PM concentrations, followed by wind speed and solar radiation. The results show that the proposed models produced better performance than the existing approaches, particularly in improving on the biases of the process-based models.

Description: 〈b〉Observational evidence of particle condensational growth in the UTLS over Tibetan Plateau〈/b〉〈br〉 Qianshan He, Jianzhong Ma, Xiangdong Zheng, Xiaolu Yan, Holger Vömel, Frank G. Wienhold, Wei Gao, Dongwei Liu, Guangming Shi, and Tiantao Cheng〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-6,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 An enhanced aerosol layer in the upper troposphere/lower stratosphere was observed by a COBALD over the Tibetan Plateau, in the summer of 2014. The Color Index of the enhanced aerosol layer indicates the prevalence of dominant fine particles with mode radius less than 0.1 μm. Except for the very small particles at low relative humidity (RHi 

Description: 〈b〉Subgrid variations of the cloud water and droplet number concentration over the tropical ocean: satellite observations and implications for warm rain simulations in climate models〈/b〉〈br〉 Zhibo Zhang, Hua Song, Po-Lun Ma, Vincent E. Larson, Minghuai Wang, Xiquan Dong, and Jianwu Wang〈br〉 Atmos. Chem. Phys., 19, 1077-1096, https://doi.org/10.5194/acp-19-1077-2019, 2019〈br〉 〈p〉One of the challenges in representing warm rain processes in global climate models (GCMs) is related to the representation of the subgrid variability of cloud properties, such as cloud water and cloud droplet number concentration (CDNC), and the effect thereof on individual precipitation processes such as autoconversion. This effect is conventionally treated by multiplying the resolved-scale warm rain process rates by an enhancement factor (〈span〉〈i〉E〈/i〉〈sub〉〈i〉q〈/i〉〈/sub〉〈/span〉) which is derived from integrating over an assumed subgrid cloud water distribution. The assumed subgrid cloud distribution remains highly uncertain. In this study, we derive the subgrid variations of liquid-phase cloud properties over the tropical ocean using the satellite remote sensing products from Moderate Resolution Imaging Spectroradiometer (MODIS) and investigate the corresponding enhancement factors for the GCM parameterization of autoconversion rate. We find that the conventional approach of using only subgrid variability of cloud water is insufficient and that the subgrid variability of CDNC, as well as the correlation between the two, is also important for correctly simulating the autoconversion process in GCMs. Using the MODIS data which have near-global data coverage, we find that 〈span〉〈i〉E〈/i〉〈sub〉〈i〉q〈/i〉〈/sub〉〈/span〉 shows a strong dependence on cloud regimes due to the fact that the subgrid variability of cloud water and CDNC is regime dependent. Our analysis shows a significant increase of 〈span〉〈i〉E〈/i〉〈sub〉〈i〉q〈/i〉〈/sub〉〈/span〉 from the stratocumulus (Sc) to cumulus (Cu) regions. Furthermore, the enhancement factor 〈span〉〈i〉E〈/i〉〈sub〉〈i〉N〈/i〉〈/sub〉〈/span〉 due to the subgrid variation of CDNC is derived from satellite observation for the first time, and results reveal several regions downwind of biomass burning aerosols (e.g., Gulf of Guinea, east coast of South Africa), air pollution (i.e., East China Sea), and active volcanos (e.g., Kilauea, Hawaii, and Ambae, Vanuatu), where the 〈span〉〈i〉E〈/i〉〈sub〉〈i〉N〈/i〉〈/sub〉〈/span〉 is comparable to or even larger than 〈span〉〈i〉E〈/i〉〈sub〉〈i〉q〈/i〉〈/sub〉〈/span〉, suggesting an important role of aerosol in influencing the 〈span〉〈i〉E〈/i〉〈sub〉〈i〉N〈/i〉〈/sub〉〈/span〉. MODIS observations suggest that the subgrid variations of cloud liquid water path (LWP) and CDNC are generally positively correlated. As a result, the combined enhancement factor, including the effect of LWP and CDNC correlation, is significantly smaller than the simple product of 〈span〉〈i〉E〈/i〉〈sub〉〈i〉q〈/i〉〈/sub〉⋅〈i〉E〈/i〉〈sub〉〈i〉N〈/i〉〈/sub〉〈/span〉. Given the importance of warm rain processes in understanding the Earth's system dynamics and water cycle, we conclude that more observational studies are needed to provide a better constraint on the warm rain processes in GCMs.〈/p〉

Description: 〈b〉Aerosol indirect effects on the temperature-precipitation scaling〈/b〉〈br〉 Nicolas Da Silva, Sylvain Mailler, and Philippe Drobinski〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1334,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 1 comment)〈br〉 Mycrophysical effects of aerosols were found to weaken precipitation in an Euro-Mediterranean area. The present numerical study quantify the processes that may be involved through the use of the temperature-precipitation relationship. It shows larger aerosol effects at low temperatures. At these temperatures, the most contributing process is the increase of atmospheric stability through an enhanced aerosol cooling effect in the lower troposphere compared to the upper troposphere.

Description: 〈b〉Observationally constrained analysis of sea salt aerosol in the marine atmosphere〈/b〉〈br〉 Huisheng Bian, Karl Froyd, Daniel M. Murphy, Jack Dibb, Mian Chin, Peter R. Colarco, Anton Darmenov, Arlindo da Silva, Tom L. Kucsera, Gregory Schill, Hongbin Yu, Paul Bui, Maximillan Dollner, Bernadett Weinzierl, and Alexander Smirnov〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-18,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 We address the GEOS-GOCART sea salt simulations constrained by NASA EVS ATom measurements, as well as those by MODIS and AERONET MAN. The study covers remote regions over the Pacific, Atlantic, and Southern Oceans from near surface to ~ 12 km altitude and covers both summer and winter seasons. Important sea salt fields, e.g. mass mixing ratio, vertical distribution, size distribution, and marine aerosol AOD, as well as their relationship to relative humidity and emissions, are examined.

Description: 〈b〉Speciated and total emission factors of particulate organics from burning western US wildland fuels and their dependence on combustion efficiency〈/b〉〈br〉 Coty N. Jen, Lindsay E. Hatch, Vanessa Selimovic, Robert J. Yokelson, Robert Weber, Arantza E. Fernandez, Nathan M. Kreisberg, Kelley C. Barsanti, and Allen H. Goldstein〈br〉 Atmos. Chem. Phys., 19, 1013-1026, https://doi.org/10.5194/acp-19-1013-2019, 2019〈br〉 Wildfires in the western US are occurring more frequently and burning larger land areas. Smoke from these fires will play a greater role in regional air quality and atmospheric chemistry than in the past. To help fire and climate modelers and atmospheric experimentalists better understand how smoke impacts the environment, we have separated, identified, classified, and quantified the thousands of organic compounds found in smoke and related their amounts emitted to fire conditions.

Description: 〈b〉Enhanced ice nucleation activity of coal fly ash aerosol particles initiated by ice-filled pores〈/b〉〈br〉 Nsikanabasi Silas Umo, Robert Wagner, Romy Ullrich, Alexei Kiselev, Harald Saathoff, Peter G. Weidler, Daniel J. Cziczo, Thomas Leisner, and Ottmar Möhler〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-7,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Annually, over 600 Tg of coal fly ash (CFA) are produced; and a significant proportion of this amount is injected into the atmosphere, which could significantly contribute to heterogeneous ice formation in clouds. This study presents an improved understanding of CFA particles' behaviour in forming ice in clouds, especially when exposed to lower temperatures before being re-circulated in the upper troposphere or entrained into the lower troposphere.

Description: 〈b〉Contrail cirrus radiative forcing for future air traffic〈/b〉〈br〉 Lisa Bock and Ulrike Burkhardt〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1294,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 The climate impact of air traffic is to a large degree caused by changes in cirrus cloudiness resulting from the formation of contrails. We use an atmospheric climate model with a contrail cirrus parameterization to investigate the climate impact of contrail cirrus for the year 2050. The strong increase in contrail cirrus radiative forcing due to the projected increase in air traffic volume cannot be compensated for by the reduction of soot emissions and by improvements in propulsion efficiency.

Description: 〈b〉Ice nucleating particles in the marine boundary layer in the Canadian Arctic during summer 2014〈/b〉〈br〉 Victoria E. Irish, Sarah J. Hanna, Megan D. Willis, Swarup China, Jennie L. Thomas, Jeremy J. B. Wentzell, Ana Cirisan, Meng Si, W. Richard Leaitch, Jennifer G. Murphy, Jonathan P. D. Abbatt, Alexander Laskin, Eric Girard, and Allan K. Bertram〈br〉 Atmos. Chem. Phys., 19, 1027-1039, https://doi.org/10.5194/acp-19-1027-2019, 2019〈br〉 Ice nucleating particles (INPs) are atmospheric particles that catalyse the formation of ice crystals in clouds. INPs influence the Earth's radiative balance and hydrological cycle. In this study we measured the concentrations of INPs in the Canadian Arctic marine boundary layer. Average INP concentrations fell within the range measured in other marine boundary layer locations. We also found that mineral dust is a more important contributor to the INP population than sea spray aerosol.

Description: 〈b〉On the diurnal, weekly, and seasonal cycles and annual trends in atmospheric CO〈sub〉2〈/sub〉 at Mount Zugspitze, Germany, during 1981–2016〈/b〉〈br〉 Ye Yuan, Ludwig Ries, Hannes Petermeier, Thomas Trickl, Michael Leuchner, Cédric Couret, Ralf Sohmer, Frank Meinhardt, and Annette Menzel〈br〉 Atmos. Chem. Phys., 19, 999-1012, https://doi.org/10.5194/acp-19-999-2019, 2019〈br〉 In this study, we presented a time series analysis of a 36-year composite CO〈sub〉2〈/sub〉 measurement record at Mount Zugspitze in Germany. Compared with other GAW observatories, Zugspitze proves to be a highly suitable site for monitoring the background levels of air components using proper data selection procedures. Detailed analyses of long-term trends and seasonality, as well as a thorough study of combined weekly periodicity and diurnal cycles, were conducted.

Description: 〈b〉Simulation of the radiative effect of haze on urban hydrological cycle using reanalysis data in Beijing〈/b〉〈br〉 Tom V. Kokkonen, Susan B. Grimmond, Sonja Murto, Huizhi Liu, Anu-Maija Sundström, and Leena Järvi〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1226,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 This is the first study to evaluate and correct the WATCH WFDEI reanalysis product in highly polluted urban environment. It gives important understanding of the uncertainties in reanalysis products in local scale urban modelling in polluted environments and identifies and corrects the most important variables in hydrological modelling. This is also the first study to examine the effects of haze on local scale urban hydrological cycle.

Description: 〈b〉Evaluation and comparison of MAIAC, DT and DB aerosol products over China〈/b〉〈br〉 Ning Liu, Bin Zou, Huihui Feng, Yuqi Tang, and Yu Liang〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1339,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 The first systematic validation and comparison of MAIAC, DT and DB AOD products across China during 2000 to 2017 is presented. In this process, the overall accuracy, land type dependence, view geometry dependence, spatiotemporal retrieval accuracy, spatial variation pattern and spatiotemporal completeness of three products are analyzed in details. In general, MAIAC achieves higher accuracy than DT and DB, but DT or DB may perform better than MAIAC under some specific land cover types or seasons.

Description: 〈b〉Multi-timescale variations of modelled stratospheric water vapor derived from three modern reanalysis products〈/b〉〈br〉 Mengchu Tao, Paul Konopka, Felix Ploeger, Xiaolu Yan, Jonathon S. Wright, Mohamadou Diallo, Stephan Fueglistaler, and Martin Riese〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-39,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 This paper examines the annual and inter-annual variations as well as long-term trend of modelled stratospheric water vapor with a Lagrangian chemical transport model driven by ERA-I, MERRA-2 and JRA-55. We find reasonable consistency among the annual cycle, QBO and the variabilities induced by ENSO and volcanic aerosols. The main discrepancies are linked to the differences in reanalysis upwelling rates in the lower stratosphere. The trends are sensitive to the reanalyses that drives the model.

Description: 〈b〉Common volume satellite studies of polar mesospheric clouds with Odin/OSIRIS tomography and AIM/CIPS nadir imaging〈/b〉〈br〉 Lina Broman, Susanne Benze, Jörg Gumbel, Ole-Martin Christensen, and Cora E. Randall〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1035,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Combining satellite observations of Polar Mesospheric Clouds are complicated due to satellite geometry and measurement technique. In this study, tomographic limb observations are compared to observations from a nadir viewing satellite using a common volume approach. We present a technique that overcomes differences in scattering conditions and observation geometry. The satellites show excellent agreement, which lays the basis for future insights into horizontal and vertical cloud processes.

Description: 〈b〉Urban population exposure to NO〈sub〉x〈/sub〉 emissions from local shipping in three Baltic Sea harbour cities – a generic approach〈/b〉〈br〉 Martin Otto Paul Ramacher, Matthias Karl, Johannes Bieser, Jukka-Pekka Jalkanen, and Lasse Johansson〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-127,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 We simulated the impact of NO〈sub〉x〈/sub〉 shipping emissions on air quality and exposure in the Baltic Sea harbour cities Rostock (Germany), Riga (Latvia) and Gdansk-Gdynia (Poland) for 2012. We found that local shipping affects total NO〈sub〉2〈/sub〉 with 22 %, 11 %, and 16 % in Rostock, Riga and Gdansk-Gdynia. Exposure to NO〈sub〉2〈/sub〉 from all emission sources was highest at home addresses (54–59 %). Emissions from shipping have a high impact on NO〈sub〉2〈/sub〉 exposure in the port area (50–80 %).

Description: 〈b〉Rate constant and secondary organic aerosol formation from the gas-phase reaction of eugenol with hydroxyl radicals〈/b〉〈br〉 Changgeng Liu, Yongchun Liu, Tianzeng Chen, Jun Liu, and Hong He〈br〉 Atmos. Chem. Phys., 19, 2001-2013, https://doi.org/10.5194/acp-19-2001-2019, 2019〈br〉 The rate constant and SOA formation for the OH-initiated reaction of eugenol were studied for the first time in an oxidation flow reactor. Significant SOA formation was observed, and SOA yield depended on precursor concentration and OH exposure. SO〈sub〉2〈/sub〉 and NO〈sub〉2〈/sub〉 both enhanced SOA yields. In addition, NO〈sub〉2〈/sub〉 participated in OH-initiated reaction and produced organic nitrates. The results could be helpful for further understanding SOA formation from the atmospheric oxidation of methoxyphenols.

Description: 〈b〉Evaluating solar radiation forecast uncertainty〈/b〉〈br〉 Minttu Tuononen, Ewan J. O'Connor, and Victoria A. Sinclair〈br〉 Atmos. Chem. Phys., 19, 1985-2000, https://doi.org/10.5194/acp-19-1985-2019, 2019〈br〉 Many applications require accurate forecasts of the amount of solar radiation reaching the surface, such as solar energy and UV radiation forecasts. This also means that cloud must be correctly forecast. We investigated the skill of these forecasts over Helsinki, Finland, using cloud and solar radiation observations. We found that there were errors in the model radiation forecast even when the clouds were correctly forecast, which we attribute to incorrect representation of the cloud properties.

Description: 〈b〉Variability of Bulk Water Vapor Content in the Marine Cloudy Boundary Layers from Microwave and Near-Infrared Imagery〈/b〉〈br〉 Luis F. Millán, Matthew D. Lebsock, and Joao Teixeira〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-4,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 The synergy of the collocated Advanced Microwave Scanning Radiometer (AMSR) and the Moderate Resolution Imaging Spectroradiometer (MODIS) provides daily global estimates of marine boundary layer water vapor. AMSR provides the total column water vapor, while MODIS provides the water vapor above the cloud layers. The difference between the two gives the vapor between the surface and the cloud top, which may be interpreted as the boundary layer water vapor.

Description: 〈b〉A proxy for atmospheric daytime gaseous sulfuric acid concentration in urban Beijing〈/b〉〈br〉 Yiqun Lu, Chao Yan, Yueyun Fu, Yan Chen, Yiliang Liu, Gan Yang, Yuwei Wang, Federico Bianchi, Biwu Chu, Ying Zhou, Rujing Yin, Rima Baalbaki, Olga Garmash, Chenjuan Deng, Weigang Wang, Yongchun Liu, Tuukka Petäjä, Veli-Matti Kerminen, Jingkun Jiang, Markku Kulmala, and Lin Wang〈br〉 Atmos. Chem. Phys., 19, 1971-1983, https://doi.org/10.5194/acp-19-1971-2019, 2019〈br〉 Gaseous sulfuric acid is one of the key precursors for atmospheric new particle formation processes, but its measurement remains challenging. This work develops an estimation method for the gaseous sulfuric acid concentration in an urban environment in China using multiple atmospheric variables that are easier to measure. The consideration of the heterogeneous formation of HONO and the subsequent photo-production of OH radicals improves the performance of the estimation method.

Description: 〈b〉On the sources and sinks of atmospheric VOCs: An integrated analysis of recent aircraft campaigns over North America〈/b〉〈br〉 Xin Chen, Dylan B. Millet, Hanwant B. Singh, Armin Wisthaler, Eric C. Apel, Elliot L. Atlas, Donald R. Blake, Steven S. Brown, John D. Crounse, Joost A. de Gouw, Frank Flocke, Alan Fried, Brian G. Heikes, Rebecca S. Hornbrook, Tomas Mikoviny, Kyung-Eun Min, Markus Müller, J. Andrew Neuman, Daniel W. O'Sullivan, Jeff Peischl, Gabriele G. Pfister, Dirk Richter, James M. Roberts, Thomas B. Ryerson, Stephen Shertz, Victoria Treadaway, Patrick R. Veres, James Walega, Carsten Warneke, Rebecca A. Washenfelder, Petter Weibring, and Bin Yuan〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-115,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Volatile organic compounds (VOCs) affect air quality and modify the lifetimes of other pollutants. We combine a high-resolution 3D atmospheric model with an ensemble of aircraft observations to perform an integrated analysis of the VOC budget over North America. We find that biogenic emissions provide the main source of VOC reactivity even in most major cities. Our findings point to key gaps in current models related to oxygenated VOCs and to the distribution of VOCs in the free troposphere.

Description: 〈b〉Characterization of Transport Regimes and the Polar Dome during Arctic Spring and Summer using in-situ Aircraft Measurements〈/b〉〈br〉 Heiko Bozem, Peter Hoor, Daniel Kunkel, Franziska Köllner, Johannes Schneider, Andreas Herber, Hannes Schulz, W. Richard Leaitch, Amir A. Aliabadi, Megan D. Willis, Julia Burkart, and Jonathan P. D. Abbatt〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-70,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 We present airborne trace gas measurements in the European and Canadian Arctic for July 2014 and April 2015. Based on CO and CO〈sub〉2〈/sub〉 in-situ data as well as 10-day kinematic back trajectories we characterize the prevailing transport regimes and derive a tracer based diagnostic for the determination of the polar dome boundary. Using the tracer derived boundary the analysis of the recent transport history of air masses within the polar dome reveals significant differerences between spring and summer.

Description: 〈b〉Importance of biogenic volatile organic compounds to acyl peroxy nitrates (APN) production in the southeastern US during SOAS 2013〈/b〉〈br〉 Shino Toma, Steve Bertman, Christopher Groff, Fulizi Xiong, Paul B. Shepson, Paul Romer, Kaitlin Duffey, Paul Wooldridge, Ronald Cohen, Karsten Baumann, Eric Edgerton, Abigail R. Koss, Joost de Gouw, Allen Goldstein, Weiwei Hu, and Jose L. Jimenez〈br〉 Atmos. Chem. Phys., 19, 1867-1880, https://doi.org/10.5194/acp-19-1867-2019, 2019〈br〉 Acyl peroxy nitrates (APN) were measured near the ground in Alabama using GC in summer 2013 to study biosphere–atmosphere interactions. APN were lower than measured in the SE USA over the past 2 decades. Historical data showed APN in 2013 was limited by NO〈sub〉〈i〉x〈/i〉〈/sub〉 and production was dominated by biogenic precursors more than in the past. Isoprene-derived MPAN correlated with isoprene hydroxynitrates as NO〈sub〉〈i〉x〈/i〉〈/sub〉-dependent products. MPAN varied with aerosol growth, but not with N-containing particles.

Description: 〈b〉Detection and classification of laminae in balloon-borne ozonesonde profiles: application to the long-term record from Boulder, Colorado〈/b〉〈br〉 Kenneth Minschwaner, Anthony T. Giljum, Gloria L. Manney, Irina Petropavlovskikh, Bryan J. Johnson, and Allen F. Jordan〈br〉 Atmos. Chem. Phys., 19, 1853-1865, https://doi.org/10.5194/acp-19-1853-2019, 2019〈br〉 We analyzed balloon measurements of ozone between the surface and 25 km altitude above Boulder, Colorado, and developed an algorithm to detect and classify layers of either unusually high or unusually low ozone. These layers range in vertical thickness from a few hundred meters to a few kilometers. We found that these laminae are an important contributor to the overall variability in ozone, especially in the transition region between the troposphere and stratosphere.

Description: 〈b〉Winter 2018 major sudden stratospheric warming impact on midlatitude mesosphere from microwave radiometer measurements〈/b〉〈br〉 Yuke Wang, Valery Shulga, Gennadi Milinevsky, Aleksey Patoka, Oleksandr Evtushevsky, Andrew Klekociuk, Wei Han, Asen Grytsai, Dmitry Shulga, Valery Myshenko, and Oleksandr Antyufeyev〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1361,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 1 comment)〈br〉 The major sudden stratospheric warming (SSW) dramatically changed atmospheric conditions from mesosphere to troposphere. This event is accompanied by a sharp increase in the stratosphere temperature and zonal wind reverse producing strong changes in surface weather. These changes affect even the midlatitude mesosphere, which is not widely covered by observations. Our newly installed microwave radiometer allowed studying mesospheric zonal wind to understand the SSW 2018 behavior at mid-latitudes.

Description: 〈b〉In-situ constraints on the vertical distribution of global aerosol〈/b〉〈br〉 Duncan Watson-Parris, Nick Schutgens, Carly Reddington, Kirsty J. Pringle, Dantong Liu, James D. Allan, Hugh Coe, Ken S. Carslaw, and Philip Stier〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1337,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 The vertical distribution of aerosol in the atmosphere affects its ability to act as cloud condensation nuclei, and changes the amount of sunlight it absorbs or reflects. Common global measurements of aerosol provide no information about this vertical distribution. Using a global collection of in-situ aircraft measurements to compare with an aerosol-climate model (ECHAM-HAM) we explore the key processes controlling this distribution and find that wet removal plays a key role.

Description: 〈b〉The role of low-level clouds in the West African monsoon system〈/b〉〈br〉 Anke Kniffka, Peter Knippertz, and Andreas H. Fink〈br〉 Atmos. Chem. Phys., 19, 1623-1647, https://doi.org/10.5194/acp-19-1623-2019, 2019〈br〉 The role of low-level clouds in the southern West Africa (SWA) energy balance and the West African monsoon system is assessed via targeted sensitivity studies with the NWP model ICON. We show for the first time that rainfall over SWA depends logarithmically on the optical thickness of low clouds, as these control the diurnal evolution of the planetary boundary layer, vertical stability and finally convection. Small variations in clouds or aerosol have a substantial impact on precipitation.

Description: 〈b〉Snow-darkening versus direct radiative effects of mineral dust aerosol on the Indian summer monsoon onset: role of temperature change over dust sources〈/b〉〈br〉 Zhengguo Shi, Xiaoning Xie, Xinzhou Li, Liu Yang, Xiaoxun Xie, Jing Lei, Yingying Sha, and Xiaodong Liu〈br〉 Atmos. Chem. Phys., 19, 1605-1622, https://doi.org/10.5194/acp-19-1605-2019, 2019〈br〉 Asian dust is one of the important components in modern and past climate change via its effects, including snow-darkening and direct radiation. We employed model experiments to evaluate these effects on Indian monsoon and found that the monsoon onset responds significantly to both. Snow-darkening effect weakens the monsoon, but direct radiative effect intensifies it. Besides the previous Tibetan Plateau studies proposed, our work highlights the importance of temperature change over dust sources.

Description: 〈b〉Influence of cloud microphysical processes on black carbon wet removal, global distributions, and radiative forcing〈/b〉〈br〉 Jiayu Xu, Jiachen Zhang, Junfeng Liu, Kan Yi, Songlin Xiang, Xiurong Hu, Yuqing Wang, Shu Tao, and George Ban-Weiss〈br〉 Atmos. Chem. Phys., 19, 1587-1603, https://doi.org/10.5194/acp-19-1587-2019, 2019〈br〉 In this study, we fully describe black carbon wet removal coupled with all cloud processes from a cloud microphysics scheme in a climate model and conduct sensitivity simulations that turn off each cloud process one at a time. We find that convective scavenging, aerosol activation, ice nucleation, evaporation of rain–snow, and below-cloud scavenging dominate wet deposition of BC. In addition, the range of direct radiative forcing derived from sensitivity simulations is large, 0.09–0.33 W m〈sup〉−2〈/sup〉.

Description: 〈b〉Free tropospheric aerosols at the Mt. Bachelor Observatory: more oxidized and higher sulfate content compared to boundary layer aerosols〈/b〉〈br〉 Shan Zhou, Sonya Collier, Daniel A. Jaffe, and Qi Zhang〈br〉 Atmos. Chem. Phys., 19, 1571-1585, https://doi.org/10.5194/acp-19-1571-2019, 2019〈br〉 Regional background aerosols in the western US were studied from a mountaintop observatory during summer. Oxygenated organics and sulfate were dominant aerosol components. However, free tropospheric aerosols were more enriched in sulfate, frequently acidic, and comprised mainly of highly oxidized low-volatility organic species. In contrast, organic aerosols in the boundary-layer-influenced air masses were less oxidized and appeared to be semivolatile.

Description: 〈b〉Heuristic Estimation of Low-Level Cloud Fraction over the Globe Based on a Decoupling Parameterization〈/b〉〈br〉 Sungsu Park and Jihoon Shin〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-104,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Cloud exerts substantial impacts on the global radiation budget and hydrological cycle. We propose a new proxy for the observed low-level cloud amount (LCA), so called, ELF (Estimated Low-level cloud fraction), and showed that ELF achieves the unprecedented best performance in diagnosing spatiotemporal variation of the observed LCA. Our study can be used to evaluate the performance of GCMs, identify the source of inaccurate simulation of LCA, and better understand climate sensitivity.

Description: 〈b〉The 2015–2016 Carbon Cycle As Seen from OCO-2 and the Global 〈i〉In Situ〈/i〉 Network〈/b〉〈br〉 Sean Crowell, David Baker, Andrew Schuh, Sourish Basu, Andrew R. Jacobson, Frederic Chevallier, Junjie Liu, Feng Deng, Liang Feng, Abhishek Chatterjee, David Crisp, Annmarie Eldering, Dylan B. Jones, Kathryn McKain, John Miller, Ray Nassar, Tomohiro Oda, Christopher O'Dell, Paul I. Palmer, David Schimel, Britton Stephens, and Colm Sweeney〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-87,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Space-based retrievals of carbon dioxide offer the potential to provide dense data in regions that are sparsely observed by the surface network. We find that flux estimates that are informed by the Orbiting Carbon Observatory-2 (OCO-2) show different character from that inferred using surface measurements in tropical land regions, particularly in Africa, with a much larger total emission and larger amplitude seasonal cycle.

Description: 〈b〉Chemical characterisation of water-soluble ions in atmospheric particulate matter on the east coast of Peninsular Malaysia〈/b〉〈br〉 Naomi J. Farren, Rachel E. Dunmore, Mohammed Iqbal Mead, Mohd Shahrul Mohd Nadzir, Azizan Abu Samah, Siew-Moi Phang, Brian J. Bandy, William T. Sturges, and Jacqueline F. Hamilton〈br〉 Atmos. Chem. Phys., 19, 1537-1553, https://doi.org/10.5194/acp-19-1537-2019, 2019〈br〉 During the winter monsoon, air quality on the east coast of Peninsular Malaysia is influenced by local emissions and aged emissions transported from highly polluted East Asian regions. Atmospheric particulate matter has been sampled at a rural coastal location, and ion chromatography has been used to make time-resolved measurements of the major atmospheric ions present. Analysis of aerosol composition and back trajectories has provided an insight into common sources and formation pathways.

Description: 〈b〉Relative humidity effect on the formation of highly oxidized molecules and new particles during monoterpene oxidation〈/b〉〈br〉 Xiaoxiao Li, Sabrina Chee, Jiming Hao, Jonathan P. D. Abbatt, Jingkun Jiang, and James N. Smith〈br〉 Atmos. Chem. Phys., 19, 1555-1570, https://doi.org/10.5194/acp-19-1555-2019, 2019〈br〉 We performed lab experiments to explore the role of relative humidity, RH, in atmospheric monoterpene oxidation and new particle formation. These studies will provide insights into the most important steps in the process, while also more accurately representing the real atmosphere. We found that the detected compounds did not change with RH, and in fact could mostly be fully explained by the autoxidation of organic peroxy radicals followed by bimolecular reactions with other peroxy radicals.

Description: 〈b〉The importance of the representation of air pollution emissions for the modeled distribution and radiative effects of black carbon in the Arctic〈/b〉〈br〉 Jacob Schacht, Bernd Heinold, Johannes Quaas, John Backman, Ribu Cherian, Andre Ehrlich, Andreas Herber, Wan Ting Katty Huang, Yutaka Kondo, Andreas Massling, P. R. Sinha, Bernadett Weinzierl, Marco Zanatta, and Ina Tegen〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-71,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 The Arctic is warming faster than the rest of Earth. Black carbon (BC) aerosol contributes to this Arctic Amplification by direct and indirect aerosol radiative effects while distributed in the air or deposited on snow and ice. The aerosol-climate model ECHAM-HAM is used to estimate the direct radiative effect (DRE). Airborne and near-surface BC measurements are used to evaluate the model and give an uncertainty range for the burden and DRE of Arctic BC caused by different emission inventories.

Description: 〈b〉Two pathways of how remote SST anomalies drive the interannual variability of autumnal haze days in the Beijing–Tianjin–Hebei region, China〈/b〉〈br〉 Jing Wang, Zhiwei Zhu, Li Qi, Qiaohua Zhao, Jinhai He, and Julian X. L. Wang〈br〉 Atmos. Chem. Phys., 19, 1521-1535, https://doi.org/10.5194/acp-19-1521-2019, 2019〈br〉 Less attention has been paid to haze weather during the autumn season. Here, we unravel the mechanism of how SST anomalies over the subtropical North Atlantic and western North Pacific drive the interannual variability of the autumnal haze days in the Beijing–Tianjin–Hebei region. The two pathways of SST anomaly forcings can result in an anticyclonic (cyclonic) anomaly over Northeast Asia, leading to a lower-level southerly (northerly) anomaly and in turn more (fewer) haze days in this region.

Description: 〈b〉Prior biosphere model impact on global terrestrial CO〈sub〉2〈/sub〉 fluxes estimated from OCO-2 retrievals〈/b〉〈br〉 Sajeev Philip, Matthew S. Johnson, Christopher Potter, Vanessa Genovesse, David F. Baker, Katherine D. Haynes, Daven K. Henze, Junjie Liu, and Benjamin Poulter〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1095,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 This research was conducted to quantify the impact of different prior global biosphere models on the estimate of terrestrial CO〈sub〉2〈/sub〉 fluxes when assimilating Orbiting Carbon Observatory-2 (OCO-2) satellite observations. To determine the prior model impact, we apply Observing System Simulation Experiments (OSSEs). Even with the substantial spatio-temporal coverage of OCO-2 data, residual differences in posterior CO〈sub〉2〈/sub〉 flux estimates remain due to the choice of prior flux mean and uncertainties.

Description: 〈b〉Impact of humidity biases on light precipitation occurrence: observations versus simulations〈/b〉〈br〉 Sophie Bastin, Philippe Drobinski, Marjolaine Chiriaco, Olivier Bock, Romain Roehrig, Clemente Gallardo, Dario Conte, Marta Domínguez Alonso, Laurent Li, Piero Lionello, and Ana C. Parracho〈br〉 Atmos. Chem. Phys., 19, 1471-1490, https://doi.org/10.5194/acp-19-1471-2019, 2019〈br〉 This paper uses colocated observations of temperature, precipitation and humidity to investigate the triggering of precipitation. It shows that there is a critical value of humidity above which precipitation picks up. This critical value depends on 〈i〉T〈/i〉 and varies spatially. It also analyses how this dependency is reproduced in regional climate simulations over Europe. Models with too little and too light precipitation have both lower critical value of humidity and higher probability to exceed it.

Description: 〈b〉Organic aerosol source apportionment in Zurich using an extractive electrospray ionization time-of-flight mass spectrometry (EESI-TOF): Part II, biomass burning influences in winter〈/b〉〈br〉 Lu Qi, Mindong Chen, Giulia Stefenelli, Veronika Pospisilova, Yandong Tong, Amelie Bertrand, Christoph Hueglin, Xinlei Ge, Urs Baltensperger, André S. H. Prévôt, and Jay G. Slowik〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-64,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Current understanding of OA sources is limited by the chemical resolution of existing real-time measurement technology. We describe the first wintertime deployment of a novel extractive electrospray ionization time-of-flight mass spectrometer, which provides near-molecular OA measurements with high time resolution. We show that biomass combustion strongly influences winter OA. Via factor analysis, aging-dependent signatures and time contributions of biomass combustion-derived OA are resolved.

Description: 〈b〉Diagnosing spatial error structures in CO〈sub〉2〈/sub〉 mole fractions and XCO〈sub〉2〈/sub〉 column mole fractions from atmospheric transport〈/b〉〈br〉 Thomas Lauvaux, Liza I. Díaz-Isaac, Marc Bocquet, and Nicolas Bousserez〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1113,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 A small-size ensemble of mesoscale simulations has been filtered to characterize the spatial structures of transport errors in atmospheric CO〈sub〉2〈/sub〉 mixing ratios. The extracted error structures in in situ and column CO〈sub〉2〈/sub〉 show similar length scales compared to other meteorological variables, including seasonality, which could be used as proxies in regional inversion systems.

Description: 〈b〉Organic coating on sulfate and soot particles in summer Arctic atmosphere〈/b〉〈br〉 Hua Yu, Weijun Li, Yangmei Zhang, Peter Tunved, Manuel Dall'Osto, Xiaojing Shen, Junying Sun, Xiaoye Zhang, and Zongbo Shi〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1205,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Interaction of anthropogenic particles with radiation and clouds plays an important role on Arctic climate change. Mixing state of different aerosols is a key parameter to influence such interaction. However, little is known on this parameter, preventing an accurate representation of this information in global models. The multi-microscopic techniques were used to find one general core-shell structure that secondary sulfate particles were covered by organic coating in arctic atmosphere.

Description: 〈b〉Impacts of meteorology and emissions on summertime surface ozone increases over central eastern China between 2003 and 2015〈/b〉〈br〉 Lei Sun, Likun Xue, Yuhang Wang, Longlei Li, Jintai Lin, Ruijing Ni, Yingying Yan, Lulu Chen, Juan Li, Qingzhu Zhang, and Wenxing Wang〈br〉 Atmos. Chem. Phys., 19, 1455-1469, https://doi.org/10.5194/acp-19-1455-2019, 2019〈br〉 We quantified the detailed impacts of meteorology and anthropogenic emissions on surface O〈sub〉3〈/sub〉 increase in central eastern China between 2003 and 2015 using GEOS-Chem. The emission change plays a more important role than the meteorological change, while the regions with a larger O〈sub〉3〈/sub〉 increase are more sensitive to meteorology. NMVOC emission change dominated the O〈sub〉3〈/sub〉 increase in eastern CEC, while NO〈sub〉〈i〉x〈/i〉〈/sub〉 emission change led to an O〈sub〉3〈/sub〉 increase in western and central CEC and O〈sub〉3〈/sub〉 decrease in urban areas.

Description: 〈b〉Viscosities, diffusion coefficients, and mixing times of intrinsic fluorescent organic molecules in brown limonene secondary organic aerosol and tests of the Stokes–Einstein equation〈/b〉〈br〉 Dagny A. Ullmann, Mallory L. Hinks, Adrian M. Maclean, Christopher L. Butenhoff, James W. Grayson, Kelley Barsanti, Jose L. Jimenez, Sergey A. Nizkorodov, Saeid Kamal, and Allan K. Bertram〈br〉 Atmos. Chem. Phys., 19, 1491-1503, https://doi.org/10.5194/acp-19-1491-2019, 2019〈br〉 We measured the viscosity and diffusion of organic molecules in secondary organic aerosol (SOA) generated from the ozonolysis of limonene. The results suggest that the mixing times of large organics in the SOA studied are short (

Description: 〈b〉Response of early winter haze in the North China Plain to autumn Beaufort sea ice〈/b〉〈br〉 Zhicong Yin, Yuyan Li, and Huijun Wang〈br〉 Atmos. Chem. Phys., 19, 1439-1453, https://doi.org/10.5194/acp-19-1439-2019, 2019〈br〉 Recently, haze pollution in the North China has been serious and disastrous. The preceding heavy autumn sea ice intensified the early winter haze pollution over North China. The results provide possibilities for the seasonal to interannual prediction of haze pollution that helps to determine whether extra stringent emission control measures are needed to counteract the effect of climate variability.

Description: 〈b〉Understanding aerosol–cloud interactions through modeling the development of orographic cumulus congestus during IPHEx〈/b〉〈br〉 Yajuan Duan, Markus D. Petters, and Ana P. Barros〈br〉 Atmos. Chem. Phys., 19, 1413-1437, https://doi.org/10.5194/acp-19-1413-2019, 2019〈br〉 A new cloud parcel model that simulates entrainment, condensational growth, and collision–coalescence processes is presented and evaluated against airborne observations in complex terrain during IPHEx. Analysis of model simulations reveals that nonlinear interactions among turbulent dispersion, activation, and droplet growth processes modulate spectral width and explain the emergence of bimodal cloud drop spectra in aircraft measurements from different cloud regions and at different heights.

Description: 〈b〉Mesospheric semidiurnal tides and near-12-hour waves through jointly analyzing five longitudinally-distributed specular meteor radars at boreal midlatitudes〈/b〉〈br〉 Maosheng He and Jorge L. Chau〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1320,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 We propose an approach to resolve waves with different spatial scales at a given frequency using ground-based detectors from few longitudinal sectors. The approach is used to study near-12-hour waves. Our results suggest that broadly-reported enhancements of two solar nonmigrating tides during sudden stratospheric warming events are just low-frequency-resolved signatures of two neighboring waves. The tides do not enhance.

Description: 〈b〉Retrieval of total column and surface NO〈sub〉2〈/sub〉 from Pandora zenith-sky measurements〈/b〉〈br〉 Xiaoyi Zhao, Debora Griffin, Vitali Fioletov, Chris McLinden, Jonathan Davies, Akira Ogyu, Sum Chi Lee, Alexandru Lupu, Michael D. Moran, Alexander Cede, Martin Tiefengraber, and Moritz Müller〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1336,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 New nitrogen dioxide (NO〈sub〉2〈/sub〉) retrieval algorithm are developed for Pandora zenith-sky measurements. A column-to-surface conversion look-up table was produced for the Pandora instruments; therefore, quick and practical Pandora-based surface NO〈sub〉2〈/sub〉 concentration data can be obtained for air quality monitoring purposes. It is demonstrated that the surface NO〈sub〉2〈/sub〉 concentration is controlled not only by the planetary boundary-layer height, but also by both boundary-layer dynamics and photochemistry.

Description: 〈b〉Simultaneous in situ measurements of small-scale structures in neutral, plasma, and atomic oxygen densities during WADIS sounding rocket project〈/b〉〈br〉 Boris Strelnikov, Martin Eberhart, Martin Friedrich, Jonas Hedin, Mikhail Khaplanov, Gerd Baumgarten, Bifford P. Williams, Tristan Staszak, Heiner Asmus, Irina Strelnikova, Ralph Latteck, Mykhaylo Grygalashvyly, Franz-Josef Lübken, Josef Höffner, Raimund Wörl, Jörg Gumbel, Stefan Löhle, Stefanos Fasoulas, Markus Rapp, Aroh Barjatya, Michael J. Taylor, and Pierre-Dominique Pautet〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1043,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Sounding rockets are the only mean of measuring small-scale structures (i.e. spatial scales of kilometers to centimeters) in the Earth's middle atmosphere (50–120 km). We present and analyze brand-new high resolution measurements of atomic oxygen (O) concentration together with high resolution measurements of ionospheric plasma and neutral air parameters. We found a new behavior of the O inside turbulent layers, which might be essential to adequately model weather and climate.

Description: 〈b〉Possible heterogeneous chemistry of hydroxymethanesulfonate (HMS) in northern China winter haze〈/b〉〈br〉 Shaojie Song, Meng Gao, Weiqi Xu, Yele Sun, Douglas R. Worsnop, John T. Jayne, Yuzhong Zhang, Lei Zhu, Mei Li, Zhen Zhou, Chunlei Cheng, Yibing Lv, Ying Wang, Wei Peng, Xiaobin Xu, Nan Lin, Yuxuan Wang, Shuxiao Wang, J. William Munger, Daniel J. Jacob, and Michael B. McElroy〈br〉 Atmos. Chem. Phys., 19, 1357-1371, https://doi.org/10.5194/acp-19-1357-2019, 2019〈br〉 Chemistry responsible for sulfate production in northern China winter haze remains mysterious. We propose a potentially key pathway through the reaction of formaldehyde and sulfur dioxide that has not been accounted for in previous studies. The special atmospheric conditions favor the formation and existence of their complex, hydroxymethanesulfonate (HMS).

Description: 〈b〉Nitrogen-containing secondary organic aerosol formation by acrolein reaction with ammonia/ammonium〈/b〉〈br〉 Zhijian Li, Sergey A. Nizkorodov, Hong Chen, Xiaohui Lu, Xin Yang, and Jianmin Chen〈br〉 Atmos. Chem. Phys., 19, 1343-1356, https://doi.org/10.5194/acp-19-1343-2019, 2019〈br〉 In this work, we found that acrolein, the smallest α,β-unsaturated aldehyde, has the potential to form light-absorbing heterocyclic secondary organic aerosol. In the gaseous phase, acrolein can react with gaseous ammonia, forming 3-picoline. In the liquid phase, the dissolved acrolein can react with ammonium to form higher molecular-weight pyridinium compounds. All the pyridinium compounds can increase the light absorptivity of aerosol particles.

Description: 〈b〉First measurement of atmospheric mercury species in Qomolangma Natural Nature Preserve, Tibetan Plateau, and evidence oftransboundary pollutant invasion〈/b〉〈br〉 Huiming Lin, Yindong Tong, Xiufeng Yin, Qianggong Zhang, Hui Zhang, Haoran Zhang, Long Chen, Shichang Kang, Wei Zhang, James Schauer, Benjamin de Foy, Xiaoge Bu, and Xuejun Wang〈br〉 Atmos. Chem. Phys., 19, 1373-1391, https://doi.org/10.5194/acp-19-1373-2019, 2019〈br〉 Located in the world's 〈q〉third Pole〈/q〉 and a remote region connecting the Indian and Eurasian plates, Qomolangma National Nature Preserve is an ideal region to study the long-range transport of atmospheric pollutants. Covering both the pre-Indian summer monsoon and Indian summer monsoon periods, our measurement and modeling results have addressed the need for more specific identification of Hg sources in this area and the importance of international cooperation regarding global mercury controls.

Description: 〈b〉On the distinctiveness of oceanic raindrop regimes〈/b〉〈br〉 David Ian Duncan, Patrick Eriksson, Simon Pfreundschuh, Christian Klepp, and Daniel C. Jones〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-34,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 Raindrop size distributions have not been systematically studied over the oceans, but are significant for remotely sensing, assimilating, and modeling rain. Here we investigate raindrop populations with new global in situ data, compare against satellite estimates, and explore a new technique to classify the shapes of these distributions. The results indicate the inadequacy of a commonly assumed shape in some regions and the sizable impact of shape variability on satellite measurements.

Description: 〈b〉Open fires in Greenland in summer 2017: transport, deposition and radiative effects of BC, OC and BrC emissions〈/b〉〈br〉 Nikolaos Evangeliou, Arve Kylling, Sabine Eckhardt, Viktor Myroniuk, Kerstin Stebel, Ronan Paugam, Sergiy Zibtsev, and Andreas Stohl〈br〉 Atmos. Chem. Phys., 19, 1393-1411, https://doi.org/10.5194/acp-19-1393-2019, 2019〈br〉 We simulated the peatland fires that burned in Greenland in summer 2017. Using satellite data, we estimated that the total burned area was 2345 ha, the fuel amount consumed 117 kt C and the emissions of BC, OC and BrC 23.5, 731 and 141 t, respectively. About 30 % of the emissions were deposited on snow or ice surfaces. This caused a maximum albedo change of 0.007 and a surface radiative forcing of 0.03–0.04 W m〈sup〉−2〈/sup〉, with local maxima of up to 0.63–0.77 W m〈sup〉−2〈/sup〉. Overall, the fires had a small impact.

Description: 〈b〉Photochemical aging of atmospherically reactive organic compounds involving brown carbon at the air-aqueous interface〈/b〉〈br〉 Siyang Li, Xiaotong Jiang, Marie Roveretto, Christian George, Ling Liu, Wei Jiang, Qingzhu Zhang, Wenxing Wang, Maofa Ge, and Lin Du〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2019-96,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 We stimulated the photochemical aging of organic film coated on aqueous aerosol in the presence of imidazole-2-carboxaldehyde, humic acid, atmospheric PM〈sub〉2.5〈/sub〉 sample and secondary organic aerosol sample from laboratory. The unsaturated lipid mixed with photosensitizer under UV irradiation produced hydroperoxides, leading to the surface area increase of organic film. Our results reveal the modification of organic film on aqueous aerosol have potential influence on the hygroscopic growth of droplet.

Description: 〈b〉Single-particle characterization of aerosols collected at a remote site in the Amazonian rainforest and an urban site in Manaus, Brazil〈/b〉〈br〉 Li Wu, Xue Li, HyeKyeong Kim, Hong Geng, Ricardo H. M. Godoi, Cybelli G. G. Barbosa, Ana F. L. Godoi, Carlos I. Yamamoto, Rodrigo A. F. de Souza, Christopher Pöhlker, Meinrat O. Andreae, and Chul-Un Ro〈br〉 Atmos. Chem. Phys., 19, 1221-1240, https://doi.org/10.5194/acp-19-1221-2019, 2019〈br〉 Aerosol samples collected at a remote site in the Amazonian rainforest (ATTO) and an urban site in Manaus, Brazil, were investigated on a single particle basis using a quantitative energy-dispersive electron probe X-ray microanalysis, suggesting the different sources and formation mechanisms of secondary aerosols, i.e., the predominant presence of sulfate at the ATTO site from mostly biogenic emissions and the elevated influences of nitrates from anthropogenic activities at the Manaus site.

Description: 〈b〉Analyzing the turbulent planetary boundary layer by remote sensing systems: the Doppler wind lidar, aerosol elastic lidar and microwave radiometer〈/b〉〈br〉 Gregori de Arruda Moreira, Juan Luis Guerrero-Rascado, Jose A. Benavent-Oltra, Pablo Ortiz-Amezcua, Roberto Román, Andrés E. Bedoya-Velásquez, Juan Antonio Bravo-Aranda, Francisco Jose Olmo Reyes, Eduardo Landulfo, and Lucas Alados-Arboledas〈br〉 Atmos. Chem. Phys., 19, 1263-1280, https://doi.org/10.5194/acp-19-1263-2019, 2019〈br〉 In this study we show the capabilities of combining different remote sensing systems (microwave radiometer – MWR, Doppler lidar – DL – and elastic lidar – EL) for retrieving a detailed picture of the PBL turbulent features. Concerning EL, in addition to analyzing the influence of noise, we explore the use of different wavelengths, which usually includes EL systems operated in extended networks, like EARLINET, LALINET, MPLNET or SKYNET.

Description: 〈b〉Aerosol hygroscopic growth, contributing factors, and impact on haze events in a severely polluted region in northern China〈/b〉〈br〉 Jun Chen, Zhanqing Li, Min Lv, Yuying Wang, Wei Wang, Yingjie Zhang, Haofei Wang, Xing Yan, Yele Sun, and Maureen Cribb〈br〉 Atmos. Chem. Phys., 19, 1327-1342, https://doi.org/10.5194/acp-19-1327-2019, 2019〈br〉 The hygroscopic growth function of aerosol particles is derived from Raman lidar, whose dependence on aerosol chemical composition is investigated using data from an aerosol chemical speciation monitor (ACSM) and a hygroscopic tandem differential mobility analyzer (H-TDMA) deployed in China. Two distinct cases were chosen with marked differences in their hygroscopic growth, which was fitted by the Kasten model. The differences were attributed to different amounts of chemical species.

Description: 〈b〉The control of anthropogenic emissions contributed to 80 % of the decrease in PM〈sub〉2.5〈/sub〉 concentrations in Beijing from 2013 to 2017〈/b〉〈br〉 Ziyue Chen, Danlu Chen, Meipo Kwan, Bin Chen, Nianliang Cheng, Bingbo Gao, Yan Zhuang, Ruiyuan Li, and Bing Xu〈br〉 Atmos. Chem. Phys. Discuss., https//doi.org/10.5194/acp-2018-1112,2019〈br〉 〈b〉Manuscript under review for ACP〈/b〉 (discussion: open, 0 comments)〈br〉 With the completion of the Beijing Five-year Clean Air Action Plan by the end of 2017, the annual mean PM〈sub〉2.5〈/sub〉 concentrations in Beijing dropped dramatically to 58.0 μg/m〈sup〉3〈/sup〉 in 2017 from 89.5 μg/m〈sup〉3〈/sup〉 in 2013. However, controversies exist to argue that favorable meteorological conditions in 2017 that helped pollution dispersion were the major factor for such rapid decrease in PM〈sub〉2.5〈/sub〉 concentrations. To comprehensively evaluate this five-year plan, we employed Kolmogorov-Zurbenko (KZ) filtering and a WRF-CMAQ model to quantify the relative contribution of meteorological conditions and the control of anthropogenic emissions to PM〈sub〉2.5〈/sub〉 reduction in Beijing from 2013 to 2017. For these five years, the relative contribution of emission-reduction measures to the decrease of PM〈sub〉2.5〈/sub〉 concentrations in Beijing calculated by KZ filtering and the WRF-CMAQ model was 80.6 % and 78.6 % respectively. The WRF-CMAQ model further revealed that local and regional emission-reduction measures contributed to 53.7 % and 24.9 % of the PM〈sub〉2.5〈/sub〉 reduction respectively. For local emission-reduction measures, the regulation of coal boilers, increasing clean fuels for residential use, industrial restructuring, the regulation of raise dust and vehicle emissions contributed to 20.1 %, 17.4 %, 10.8 %, 3.0 % and 2.4 % of PM〈sub〉2.5〈/sub〉 reduction respectively. Both models suggested that the control of anthropogenic emissions contributed to around 80 % of the total decrease in PM〈sub〉2.5〈/sub〉 concentrations in Beijing, indicating that emission control was crucial for the notable improvement in air quality in Beijing from 2013 to 2017. Therefore, such long-term air quality clean plan should be continued for the future years to further reduce PM〈sub〉2.5〈/sub〉 concentrations in Beijing. Considering that different emission-reduction measures exert distinct effects on PM〈sub〉2.5〈/sub〉 reduction and existing emission-reduction measures work poorly to reduce ozone concentrations, future strategies for emission-reduction should be designed and implemented accordingly.

Description: 〈b〉The observed diurnal cycle of low-level stratus clouds over southern West Africa: a case study〈/b〉〈br〉 Karmen Babić, Bianca Adler, Norbert Kalthoff, Hendrik Andersen, Cheikh Dione, Fabienne Lohou, Marie Lothon, and Xabier Pedruzo-Bagazgoitia〈br〉 Atmos. Chem. Phys., 19, 1281-1299, https://doi.org/10.5194/acp-19-1281-2019, 2019〈br〉 The first detailed observational analysis of the complete diurnal cycle of low-level clouds (LLC) and associated atmospheric processes over southern West Africa is performed using the data gathered within the DACCIWA (Dynamics-Aerosol-Chemistry-Cloud-Interactions in West Africa) ground-based campaign. We find cooling related to the horizontal advection, which occurs in connection with the inflow of cool maritime air mass and a prominent low-level jet, to have the dominant role in LLC formation.