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  • 1
    Publication Date: 2015-02-10
    Description: Multiyear simulations with the atmospheric chemistry general circulation model EMAC with a microphysical modal aerosol module at high vertical resolution demonstrate that the sulfur gases COS and SO 2 , the latter from low-latitude and midlatitude volcanic eruptions, predominantly control the formation of stratospheric aerosol. Marine dimethyl sulfide (DMS) and other SO 2 sources, including strong anthropogenic emissions in China, are found to play a minor role except in the lowermost stratosphere. Estimates of volcanic SO 2 emissions are based on satellite observations using TOMS and OMI for total injected mass and MIPAS on ENVISAT or SAGE for the spatial distribution. The 10 year SO 2 and COS dataset of MIPAS is also used for model evaluation. The calculated radiative forcing of stratospheric background aerosol including sulfate from COS and small contributions by DMS oxidation, and organic aerosol from biomass burning, is about 0.07 W/m 2 . For stratospheric sulfate aerosol from medium and small volcanic eruptions between 2005 and 2011 a global radiative forcing up to 0.2 W/m 2 is calculated, moderating climate warming, while for the major Pinatubo eruption the simulated forcing reaches 5 W/m 2 , leading to temporary climate cooling. The Pinatubo simulation demonstrates the importance of radiative feedback on dynamics, e.g., enhanced tropical upwelling, for large volcanic eruptions.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
    Publication Date: 2012-10-04
    Description: We investigate the upper tropospheric distribution of methane (CH4) at low latitudes based on the analysis of air samples collected from aboard passenger aircraft. The distribution of CH4 exhibits spatial and seasonal differences, such as the pronounced seasonal cycles over tropical Asia and elevated mixing ratios over central Africa. Over Africa, the correlations of methane, ethane, and acetylene with carbon monoxide indicate that these high mixing ratios originate from biomass burning as well as from biogenic sources. Upper tropospheric mixing ratios of CH4 were modeled using a chemistry transport model. The simulation captures the large-scale features of the distributions along different flight routes, but discrepancies occur in some regions. Over Africa, where emissions are not well constrained, the model predicts a too steep interhemispheric gradient. During summer, efficient convective vertical transport and enhanced emissions give rise to a large-scale CH4 maximum in the upper troposphere over subtropical Asia. This seasonal (monsoonal) cycle is analyzed with a tagged tracer simulation. The model confirms that in this region convection links upper tropospheric mixing ratios to regional sources on the Indian subcontinent, subtropical East Asia, and Southeast Asia. This type of aircraft data can therefore provide information about surface fluxes.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
    Publication Date: 2012-06-20
    Description: This paper presents an intercomparison and evaluation of gridded temperature and precipitation data sets, based on observations in the Mediterranean and the Middle East region. Using available global and regional data, we investigate the spatial and seasonal distributions of these two parameters, including uncertainties and trends for eight subregions that signify distinct climate regimes. All data sets represent the overall spatial features well though partly with biases. Using the seasonal means, standard deviations and cumulative density functions for the eight subregions, we identify outliers among the data sets. The correlations between data sets are high except for some regional data products. Desert areas such as Saudi Arabia and Libya-Egypt appear problematic due to their sparse station network. Similar upward trends of temperature and downward trends in precipitation are found for most of the region in all data sets, while differences appear in their magnitude and level of significance.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
    Publication Date: 2012-02-29
    Description: Hydroxyl radical buffered by isoprene oxidation over tropical forests Nature Geoscience 5, 190 (2012). doi:10.1038/ngeo1405 Authors: D. Taraborrelli, M. G. Lawrence, J. N. Crowley, T. J. Dillon, S. Gromov, C. B. M. Groß, L. Vereecken & J. Lelieveld The hydroxyl radical is a key oxidant in the Earth’s atmosphere. This short-lived highly reactive molecule plays an important role in the degradation of volatile organic compounds, leading to the production of ozone and the formation and growth of aerosol particles. In this way, hydroxyl radicals influence air quality and regional climate. Measurements over tropical forests suggest that hydroxyl radicals are recycled following reaction with the volatile organic compound isoprene, but the chemistry underpinning this observation is uncertain. Here, we propose a detailed chemical mechanism for the oxidation of isoprene by hydroxyl radicals. The photo-oxidation of unsaturated hydroperoxy-aldehydes—a product of isoprene oxidation—is a central part of the mechanism; their photolysis initiates a hydroxyl radical production cascade that is limited by the reaction of hydroperoxy-aldehydes with the hydroxyl radical itself. We incorporate this mechanism into a global atmospheric chemistry model and find that measurements of hydroxyl radical concentrations over a pristine region of the Amazon, and in moderately polluted conditions, are captured well. On the basis of this agreement, we suggest that isoprene oxidation can buffer hydroxyl radical concentrations, by serving as both a sink and source for these radicals.
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 5
    Publication Date: 2013-10-22
    Description: [1]  We investigate the vertical transport of atmospheric chemical reactants from the sub-cloud layer to the cumulus cloud layer driven by shallow convection over the Amazon during the dry season. The dynamical and chemical assumptions needed for mesoscale and global chemistry-transport model parametrizations are systematically analysed using a Large-Eddy Simulation model. We quantify the mass-flux transport contribution to the temporal evolution of reactants. Isoprene, a key atmospheric compound over the tropical rain forest, decreases by 8.5 % hr − 1 on average and 15 % hr − 1 at maximum due to mass-flux induced removal. We apply mass-flux parametrizations for the transport of chemical reactants and obtain satisfactory agreement with numerically resolved transport, except for some reactants like O 3 , NO and NO 2 . The latter is caused by the local partitioning of reactants, influenced by UV radiation extinction by clouds and small-scale variability of ambient atmospheric compounds. By considering the longer lived NO x (NO + NO 2 ), the transport is well represented by the parametrization. Finally, by considering heterogeneous surface exchange conditions, it is demonstrated that the parametrizations are sensitive to boundary conditions due to changes in the boundary-layer dynamics.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Publication Date: 2012-03-31
    Description: Hydroxyl radical buffered by isoprene oxidation over tropical forests Nature Geoscience 5, 300 (2012). doi:10.1038/ngeo1433 Authors: D. Taraborrelli, M. G. Lawrence, J. N. Crowley, T. J. Dillon, S. Gromov, C. B. M. Groß, L. Vereecken & J. Lelieveld
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 7
    Publication Date: 2012-02-10
    Description: Recent studies have shown that measured OH under NOx-limited, high-isoprene conditions are many times higher than modeled OH. In this study, a detailed analysis of the HOx radical budgets under low-NOx, rural conditions was performed employing a box model based on the Master Chemical Mechanism (MCMv3.2). The model results were compared with HOx radical measurements performed during the international HOxComp campaign carried out in Jülich, Germany, during summer 2005. Two different air masses influenced the measurement site denoted as high-NOx (NO, 1–3 ppbv) and low-NOx (NO, 〈 1 ppbv) periods. Both modeled OH and HO2 diurnal profiles lay within the measurement range of all HOx measurement techniques, with correlation slopes between measured and modeled OH and HO2 around unity. Recently discovered interference in HO2 measurements caused by RO2 cross sensitivity was found to cause a 30% increase in measured HO2 during daytime on average. After correction of the measured HO2 data, the model HO2 is still in good agreement with the observations at high NOx but overpredicts HO2 by a factor of 1.3 to 1.8 at low NOx. In addition, for two different set of measurements, a missing OH source of 3.6 ± 1.6 and 4.9 ± 2.2 ppb h−1 was estimated from the experimental OH budget during the low-NOx period using the corrected HO2 data. The measured diurnal profile of the HO2/OH ratio, calculated using the corrected HO2, is well reproduced by the MCM at high NOx but is significantly overestimated at low NOx. Thus, the cycling between OH and HO2 is better described by the model at high NOx than at low NOx. Therefore, similar comprehensive field measurements accompanied by model studies are urgently needed to investigate HOx recycling under low-NOx conditions.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
    Publication Date: 2001-02-13
    Description: The Indian Ocean Experiment (INDOEX) was an international, multiplatform field campaign to measure long-range transport of air pollution from South and Southeast Asia toward the Indian Ocean during the dry monsoon season in January to March 1999. Surprisingly high pollution levels were observed over the entire northern Indian Ocean toward the Intertropical Convergence Zone at about 6 degrees S. We show that agricultural burning and especially biofuel use enhance carbon monoxide concentrations. Fossil fuel combustion and biomass burning cause a high aerosol loading. The growing pollution in this region gives rise to extensive air quality degradation with local, regional, and global implications, including a reduction of the oxidizing power of the atmosphere.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lelieveld, J -- Crutzen, P J -- Ramanathan, V -- Andreae, M O -- Brenninkmeijer, C M -- Campos, T -- Cass, G R -- Dickerson, R R -- Fischer, H -- de Gouw, J A -- Hansel, A -- Jefferson, A -- Kley, D -- de Laat, A T -- Lal, S -- Lawrence, M G -- Lobert, J M -- Mayol-Bracero, O L -- Mitra, A P -- Novakov, T -- Oltmans, S J -- Prather, K A -- Reiner, T -- Rodhe, H -- Scheeren, H A -- Sikka, D -- Williams, J -- New York, N.Y. -- Science. 2001 Feb 9;291(5506):1031-6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Max-Planck-Institute for Chemistry, Post Office Box 3060, D-55020 Mainz, Germany. lelieveld@mpch-mainz.mpg.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11161214" target="_blank"〉PubMed〈/a〉
    Keywords: Aerosols ; Agriculture ; *Air Pollution ; Asia ; Asia, Southeastern ; Atmosphere ; Biomass ; Carbon ; Carbon Monoxide ; Coal Ash ; Fossil Fuels ; Industrial Waste ; Nitrogen Oxides ; Oceans and Seas ; Ozone ; Particulate Matter ; Seasons
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 9
    Publication Date: 2002-10-26
    Description: The Mediterranean Intensive Oxidant Study, performed in the summer of 2001, uncovered air pollution layers from the surface to an altitude of 15 kilometers. In the boundary layer, air pollution standards are exceeded throughout the region, caused by West and East European pollution from the north. Aerosol particles also reduce solar radiation penetration to the surface, which can suppress precipitation. In the middle troposphere, Asian and to a lesser extent North American pollution is transported from the west. Additional Asian pollution from the east, transported from the monsoon in the upper troposphere, crosses the Mediterranean tropopause, which pollutes the lower stratosphere at middle latitudes.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lelieveld, J -- Berresheim, H -- Borrmann, S -- Crutzen, P J -- Dentener, F J -- Fischer, H -- Feichter, J -- Flatau, P J -- Heland, J -- Holzinger, R -- Korrmann, R -- Lawrence, M G -- Levin, Z -- Markowicz, K M -- Mihalopoulos, N -- Minikin, A -- Ramanathan, V -- De Reus, M -- Roelofs, G J -- Scheeren, H A -- Sciare, J -- Schlager, H -- Schultz, M -- Siegmund, P -- Steil, B -- Stephanou, E G -- Stier, P -- Traub, M -- Warneke, C -- Williams, J -- Ziereis, H -- New York, N.Y. -- Science. 2002 Oct 25;298(5594):794-9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Max Planck Institute for Chemistry, Post Office Box 3060, 55020 Mainz, Germany. lelieveld@mpch-mainz.mpg.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/12399583" target="_blank"〉PubMed〈/a〉
    Keywords: Aerosols ; *Air Pollutants ; *Air Pollution ; Asia ; Atmosphere ; *Carbon Monoxide ; Climate ; Europe ; Mediterranean Region ; North America ; Ozone ; Weather
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 10
    Publication Date: 2008-04-11
    Description: Terrestrial vegetation, especially tropical rain forest, releases vast quantities of volatile organic compounds (VOCs) to the atmosphere, which are removed by oxidation reactions and deposition of reaction products. The oxidation is mainly initiated by hydroxyl radicals (OH), primarily formed through the photodissociation of ozone. Previously it was thought that, in unpolluted air, biogenic VOCs deplete OH and reduce the atmospheric oxidation capacity. Conversely, in polluted air VOC oxidation leads to noxious oxidant build-up by the catalytic action of nitrogen oxides (NO(x) = NO + NO2). Here we report aircraft measurements of atmospheric trace gases performed over the pristine Amazon forest. Our data reveal unexpectedly high OH concentrations. We propose that natural VOC oxidation, notably of isoprene, recycles OH efficiently in low-NO(x) air through reactions of organic peroxy radicals. Computations with an atmospheric chemistry model and the results of laboratory experiments suggest that an OH recycling efficiency of 40-80 per cent in isoprene oxidation may be able to explain the high OH levels we observed in the field. Although further laboratory studies are necessary to explore the chemical mechanism responsible for OH recycling in more detail, our results demonstrate that the biosphere maintains a remarkable balance with the atmospheric environment.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lelieveld, J -- Butler, T M -- Crowley, J N -- Dillon, T J -- Fischer, H -- Ganzeveld, L -- Harder, H -- Lawrence, M G -- Martinez, M -- Taraborrelli, D -- Williams, J -- England -- Nature. 2008 Apr 10;452(7188):737-40. doi: 10.1038/nature06870.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Max Planck Institute for Chemistry, 27 Becherweg, 55128 Mainz, Germany. lelieveld@mpch-mainz.mpg.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18401407" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Atlantic Ocean ; Atmosphere/*chemistry ; Butadienes/metabolism ; French Guiana ; Guyana ; Hemiterpenes/metabolism ; Hydroxyl Radical/metabolism ; Nitric Oxide/metabolism ; Oxidation-Reduction ; Ozone/analysis ; Pentanes/metabolism ; Suriname ; Trees/*metabolism ; *Tropical Climate
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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