ALBERT

Description: Atmospheric aerosol has a great influence on human health and the natural environment as well as the weather and climate system. Therefore, atmospheric aerosol has attracted significant attention from the society as a whole. Despite consistent research efforts, there are still uncertainties in our understanding of its effects due to poor knowledge of aerosol vertical transport caused by our limited measurement capability of aerosol mass vertical transport flux. In this paper, a new method for measuring atmospheric aerosol vertical transport flux is developed based on the similarity theory of surface layer. The theoretical results show that aerosol mass flux can be linked to the real and imaginary parts of the atmospheric equivalent refractive index structure parameter (AERISP), and the ratio of aerosol mass concentration to the imaginary part of the atmospheric equivalent refractive index (AERI). The real and imaginary parts of AERISP can be measured based on the light propagation theory. The ratio of aerosol mass concentration to the imaginary part of AERI can be measured based on the measurements of aerosol mass concentration and visibility. The observational results show that aerosol vertical transport flux varies diurnally and is related to the aerosol spatial distribution. The maximum aerosol flux during the experimental period in Hefei City was 0.017 mgm−2s−1, and the mean value was 0.004 mgm−2s−1. The new method offers an effective way to study aerosol vertical transport over complex environments.

Description: Hydrogeochemistry of 10 hot springs in the Kangding district was investigated by analyzing cation and anion concentrations in the spring water. The water samples were collected in the 5 days after the Lushan MS = 7.0 earthquake, which occurred on 20 April 2013. The spring waters are classified into seven chemical types based on their hydrochemical compositions. Compared with hydrochemical data before the Lushan earthquake, concentrations of Ca2+, HCO3- and total dissolved solid (TDS) in water samples from the Guanding, Erdaoqiao, Gonghe, Erhaoying, Tianwanhe and Caoke springs significantly increased, which may be the result of a greater increase in groundwater from carbonate rocks, and water–carbonate rock interactions, enhanced by the increment of CO2. Concentrations of Na+, Cl- and SO42- in water samples from the Guanding, Zheduotang, Xinxing and Gonghe springs decreased, indicating a dilution of shallow waters. Concentrations of Na+ and SO42- in water samples from the Erhaoying spring water increased, which may be attributed to water–granite interactions enhanced by H2S. The results indicated that hydrochemical components of spring water could be used as an effective indicator for earthquakes.

Description: Emissions inventories of black carbon (BC), which are traditionally constructed using a "bottom-up" approach based on activity data and emissions factors, are considered to contain a large level of uncertainty. In this paper, an ensemble optimal interpolation (EnOI) data assimilation technique is used to investigate the possibility of optimally recovering the spatially resolved emissions bias of BC. An inverse modeling system for emissions is established for an atmospheric chemistry aerosol model and two key problems related to ensemble data assimilation in the top-down emissions estimation are discussed: (1) how to obtain reasonable ensembles of prior emissions; and (2) establishing a scheme to localize the background-error matrix. An experiment involving a one month simulation cycle with EnOI inversion of BC emissions is performed for January 2008. The bias of the BC emissions intensity in China at each grid point is corrected by this inverse system. The inversed emission over China in January is 240.1 Gg, and annual emission is about 2750 Gg, which is over 1.8 times of bottom-up emission inventory. The results show that, even though only monthly mean BC measurements are employed to inverse the emissions, the accuracy of the daily model simulation improves. Using top-down emissions, the average root-mean-square error of simulated daily BC is decreased by nearly 30 %. These results are valuable and promising for a better understanding of aerosol emissions and distributions, as well as aerosol forecasting.

Description: In a companion paper (Jing et al., 2015), a high temporal–spatial resolution vehicle emission inventory (HTSVE) for 2013 in Beijing has been established based on near real time (NRT) traffic data and bottom up methodology. In this study, based on the sensitivity analysis method of switching on/off pollutant emissions in the Chinese air quality forecasting model CUACE, a modeling study was carried out to evaluate the contributions of vehicle emission to the air pollution in Beijing main urban areas in the periods of summer (July) and winter (December) 2013. Generally, CUACE model had good performance of pollutants concentration simulation. The model simulation has been improved by using HTSVE. The vehicle emission contribution (VEC) to ambient pollutant concentrations not only changes with seasons but also changes over moment. The mean VEC, affected by regional pollutant transports significantly, is 55.4 and 48.5 % for NO2, while 5.4 and 10.5 % for PM2.5 in July and December 2013, respectively. Regardless of regional transports, relative vehicle emission contribution (RVEC) to NO2 is 59.2 and 57.8 % in July and December 2013, while 8.7 and 13.9 % for PM2.5. The RVEC to PM2.5 is lower than PM2.5 contribution rate for vehicle emission in total emission, which may be caused by easily dry deposition of PM2.5 from vehicle emission in near-surface layer compared to elevated source emission.

Description: The aim of this investigation was to obtain a better understanding of the variability of the cloud condensation nuclei (CCN) activity during new particle formation (NPF) events in an anthropogenically polluted atmosphere of the North China Plain (NCP). We investigated the size-resolved activation ratio as well as particle number size distribution, hygroscopicity and chemical composition during an intensive field experiment at a regional atmospheric observatory at Xianghe. Interestingly, two types of NPF events were found, in which the growth of the newly formed particles is dominated by either sulfate or organic matters. The particle CCN activity therefore significantly differs in those NPF events, indicating that it might be difficult to find a simple parameterization of particle CCN activity during NPF events over the NCP. For an accurate estimation of the potential CCN number concentration (NCCN) during NPF events, the variation of CCN activity has to be taken into account. Considering that a fixed activation ratio curve or critical diameter are usually used to calculate NCCN, the influence of the variation of particle CCN activity on the calculation of NCCN during NPF events was evaluated based on these two parameterizations. It was found that NCCN might be underestimated by up to 30 % if a fix activation ratio curve (representative of the region and season) is used in the calculation; and might be underestimated by up to 50 % if a fix critical diameter (representative of the region and season) is used. Therefore, we suggest not using a fixed critical diameter in the prediction of NCCN in NPF seasons. If real-time CCN activity data is not available, using a proper fixed activation ratio curve can be a compromising choice.

Description: We use the Global Modeling Initiative (GMI) modeling framework to assess the utility of cosmogenic beryllium-7 (7Be), a natural aerosol tracer, for evaluating cross-tropopause transport in global models. The GMI chemical transport model (CTM) was used to simulate atmospheric 7Be distributions using four different meteorological data sets (GEOS1-STRAT DAS, GISS II' GCM, fvGCM, and GEOS4-DAS), featuring significantly different stratosphere–troposphere exchange (STE) characteristics. The simulations were compared with the upper troposphere/lower stratosphere (UT/LS) 7Be climatology constructed from ~ 25 years of aircraft and balloon data, as well as climatological records of surface concentrations and deposition fluxes. Comparison of the fraction of surface air of stratospheric origin estimated from the 7Be simulations with observationally-derived estimates indicates excessive cross-tropopause transport at middle latitudes in simulations using GEOS1-STRAT and at high latitudes using GISS II' meteorological data. These simulations also overestimate 7Be deposition fluxes at middle latitudes (GEOS1-STRAT) and at high latitudes (GISS II'), respectively. We show that excessive cross-tropopause transport of 7Be corresponds to overestimated stratospheric contribution to tropospheric ozone. Our perspectives on STE in these meteorological fields based on 7Be simulations are consistent with previous modeling studies of tropospheric ozone using the same meteorological fields. We further apply observational constraints to other global models including GFDL AM2 and GEOS-Chem (driven by GEOS3-DAS and GEOS5-DAS). We conclude that the observational constraints for 7Be and observed 7Be total deposition fluxes can be used routinely as a first-order assessment of cross-tropopause transport in global models.

Description: While nocturnal Low-Level Jets (NLLJs) occur frequently in many parts of the world, the occurrence and other detailed characteristics of NLLJs over the Taklimakan Desert (TD) are not well known. This paper presents a climatology of NLLJs and coincident dust over the TD by analyzing multi-year ERA-Interim reanalysis and satellite observations. It is found that the ERA-Interim dataset can capture the NLLJs feature well by comparing with radiosonde data from two surface sites. The NLLJs occur in more than 60 % of nights, which are primarily easterly to east-northeasterly. They typically appear at 100 to 400 m above the surface with a speed of 4 to 10 ms−1. Most NLLJs are located above the nocturnal inversion during warm season while they are embedded in the inversion layer during cold season. NLLJs above the inversion have a strong annual cycle with a maximum frequency in August. We also quantify the convective boundary layer (CBL) height and construct an index to measure the magnitude of the momentum in the CBL. We find that the NLLJ contains more momentum than without NLLJ, and in warm season the downward momentum transfer process is more intense and rapid. The winds below the NLLJ core to the desert surface gain strength in summer and autumn, which are coincident with an enhancement of aerosol optical depth. It indicates that the NLLJ is an important mechanism for dust emission and transport during the warm season over the Taklimakan.

Description: Since individuals experienced persistent haze-fog events in January 2013 in central-eastern China, questions on factors causing differences in drastic changes in 2013 from those in adjacent years have been raised. Changes in major chemical components of aerosol particles over the years also remain unclear. The extent of meteorological factors contributed to such changes is yet to be determined. The study intends to present the changes in daily-based major water-soluble constituents, carbonaceous species and mineral aerosol in PM10 at 13 stations within different haze regions in China from 2006 to 2013, associated with specific meteorological conditions that are highly related with aerosol pollution (parameterized as an index called "PLAM"). No obvious changes were found in annual mean concentrations of these various chemical components and PM10 in 2013, relative to 2012. By contrast, wintertime mass of these components were quite different, in Hua Bei Plain (HBP), sulfate, OC, nitrate, ammonium, EC, and mineral dust concentrations in winter were approximately 43, 55, 28, 23, 21 and 130 μg m−3, respectively; these masses were approximately two to four times higher than those in background mass, also exhibiting a decline during 2006 to 2010, and then a rise till 2013. The mass of these concentrations and PM10, except mineral, respectively increased by approximately 28 to 117 and 25 % in January 2013 compared with that in January 2012. Thus, persistent haze-fog events occurred in January 2013, and approximately 60 % of this increase in component concentrations from 2012 to 2013 can be attributed to severe meteorological conditions in the winter of 2013. In Yangtzi River Delta (YRD) area, winter masses of these components, unlike HBP, did not significantly increase since 2010; PLAM was also maintained at a similar level without significant changes. In the Pearl River Delta (PRD) area, the regional background concentrations of the major chemical components were similar to those in YRD; accounted approximately 60–80 % of these in HBP. Since 2010, a decline was found for winter concentrations, which can be partially attributable to a persistent bettering meteorological conditions and the emission cutting with an emphasis on coal-combustion in this area. In addition to the scattered and centralized coal-combustion for heating, burning biomass fuel contributed to the large increase in the concentrations of carbonaceous aerosol in major haze regions, except in PRD, in winter. No obvious changes were found for the proportions of each chemical components of PM10 from 2006 to 2013. Among all of the emissions recorded in chemical compositions in 2013, coal-combustion was still the largest anthropogenic source of aerosol pollution in various areas in China, with higher sulphate proportion of PM10 in most areas of China. OC normally ranked the third. PM10 concentration increased by approximately 25 % in January of 2013 relative to 2012 that caused persistent haze-fog events in HBP; emission also reduced by approximately 35 % in Beijing and its vicinity (BIV) in late fall of 2014, thereby producing "APEC" blue; thus one can expect that the persistent haze-fog events would be reduced significantly in the BIV, if ~ one-third of the 2013 winter emission could be reduced, which can also be viewed as the upper limit of atmospheric aerosol pollution capacity in this area.

Description: Global reactive nitrogen (Nr) deposition to terrestrial ecosystems has increased dramatically since the industrial revolution. This is especially true in recent decades in China due to continuous economic growth. However, there are no comprehensive reports of both measured dry and wet Nr deposition across China. We therefore conducted a multiple-year study during the period mainly from 2010 to 2014 to monitor atmospheric concentrations of five major Nr species of gaseous NH3, NO2 and HNO3, and inorganic nitrogen (NH4+ and NO3−) in both particles and precipitation, based on a Nationwide Nitrogen Deposition Monitoring Network (NNDMN, covering 43 sites) in China. Wet deposition fluxes of Nr species were measured directly; dry deposition fluxes were estimated using airborne concentration measurements and inferential models. Our observations reveal large spatial variations of atmospheric Nr concentrations and dry and wet Nr deposition. The annual average concentrations (1.3–47.0 μg N m−3) and dry plus wet deposition fluxes (2.9–75.2 kg N ha−1 yr−1) of inorganic Nr species ranked by region as North China 〉 Southeast China 〉 Southwest China 〉 Northeast China 〉 Northwest China 〉 the Tibetan Plateau or by land use as urban 〉 rural 〉 background sites, reflecting the impact of anthropogenic Nr emission. Average dry and wet N deposition fluxes were 18.5 and 19.3 kg N ha−1 yr−1, respectively, across China, with reduced N deposition dominating both dry and wet deposition. Our results suggest atmospheric dry N deposition is equally important to wet N deposition at the national scale and both deposition forms should be included when considering the impacts of N deposition on environment and ecosystem health.

Description: Concentrations of leaf nitrogen (N) and phosphorus (P) are key leaf traits in ecosystem functioning and dynamics. Foliar stoichiometry varies remarkably among life forms. However, previous studies have focused on trees and grasses, leaving the knowledge gap for the stoichiometric patterns of shrubs. In this study, we explored the intra- and interspecific variations of leaf N and P concentration in relation to climate, soil property and evolutionary history based on 1486 samples composed of 163 shrub species from 361 shrubland sites in northern China expanding 46.1° (86.7–132.8° E) in longitude and 19.8° (32.6–52.4° N) in latitude. The results showed that leaf N concentration decreased with precipitation, leaf P concentration decreased with temperature and increased with precipitation and soil P concentration. Both leaf N and P concentrations were phylogenetically conserved, but leaf P concentration was less conserved than leaf N concentration. At community level, climates explained more interspecific, while soil nutrient explained more intraspecific, variation of leaf nutrient concentrations. These results suggested that leaf N and P concentrations responded to climate, soil, and phylogeny in different ways. Climate influenced the community chemical traits through the shift in species composition, whereas soil directly influenced the community chemical traits.