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  • 1
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    Distribution of methane in the tropical upper troposphere measured by CARIBIC and CONTRAIL aircraft (2012)
    Wiley
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    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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  • 2
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    Intercomparison of temperature and precipitation data sets based on observations in the Mediterranean and the Middle East (2012)
    Wiley
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    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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  • 3
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    Hydroxyl radical buffered by isoprene oxidation over tropical forests (2012)
    Springer Nature
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    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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  • 4
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    Quantifying the transport of sub-cloud layer reactants by shallow cumulus clouds over the Amazon (2013)
    Wiley
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    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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  • 5
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    Hydroxyl radical buffered by isoprene oxidation over tropical forests (2012)
    Springer Nature
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    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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  • 6
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    HOx budgets during HOxComp: A case study of HOx chemistry under NOx-limited conditions (2012)
    Wiley
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    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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  • 7
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    Atmospheric chemistry: A missing sink for radicals (2010)
    Nature Publishing Group (NPG)
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    Publication Date: 2010-08-21
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lelieveld, Jos -- England -- Nature. 2010 Aug 19;466(7309):925-6. doi: 10.1038/466925a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20725025" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 8
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    Small interannual variability of global atmospheric hydroxyl (2011)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2011-01-08
    Description: The oxidizing capacity of the global atmosphere is largely determined by hydroxyl (OH) radicals and is diagnosed by analyzing methyl chloroform (CH(3)CCl(3)) measurements. Previously, large year-to-year changes in global mean OH concentrations have been inferred from such measurements, suggesting that the atmospheric oxidizing capacity is sensitive to perturbations by widespread air pollution and natural influences. We show how the interannual variability in OH has been more precisely estimated from CH(3)CCl(3) measurements since 1998, when atmospheric gradients of CH(3)CCl(3) had diminished as a result of the Montreal Protocol. We infer a small interannual OH variability as a result, indicating that global OH is generally well buffered against perturbations. This small variability is consistent with measurements of methane and other trace gases oxidized primarily by OH, as well as global photochemical model calculations.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Montzka, S A -- Krol, M -- Dlugokencky, E -- Hall, B -- Jockel, P -- Lelieveld, J -- New York, N.Y. -- Science. 2011 Jan 7;331(6013):67-9. doi: 10.1126/science.1197640.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉NOAA Earth System Research Laboratory, Boulder, CO 80305, USA. stephen.a.montzka@noaa.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21212353" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 9
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    Significant concentrations of nitryl chloride observed in rural continental Europe associated with the influence of sea salt chloride and anthropogenic emissions (2012)
    Wiley
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    Publication Date: 2012-05-26
    Description: We present the first measurements of nitryl chloride (ClNO2) over continental Europe. Significant quantities of ClNO2, up to 800 pptv, were measured at a mountaintop field site in Hessen, southwest Germany. ClNO2 was detected during the majority of nights between the 15th August and 16th September 2011, its largest mixing ratios being associated with air masses influenced by sea salt and anthropogenic NOx emissions. ClNO2 persisted in measurable quantities until early afternoons on days with low photolysis frequencies. As a consequence, early morning production rates of Cl atoms could significantly exceed the production of OH via ozone photolysis, likely leading to increased O3 production.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
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    Economic Crisis Detected from Space: Air Quality observations over Athens/Greece (2013)
    Wiley
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    Publication Date: 2013-01-06
    Description: [1]  Using both satellite observations of tropospheric NO 2 columns and a number of economic metrics we investigate the impact of the economic crisis (from 2008 onward) on air quality over Greece, and Athens in particular. The multiannual analysis shows that NO 2 columns over Athens have been significantly reduced in the range 30-40%. This decline is further supported by surface measurements of atmospheric NO 2 mixing ratios. Additionally, the declining local concentrations of NO, CO, SO 2 are associated with an increase in ozone due to reduced titration by NO. In particular, regression analysis revealed that the reduction of NO 2 (0.3 ± 0.2 ppbv y -1 ) and SO 2 (0.2 ± 0.1 ppbv y -1 ) during the period 2000-2007, significantly accelerated during the economic crisis period (from 2008 onward), reaching 2.3 ± 0.2 ppbv y -1 and 0.7 ± 0.1 ppbv y -1 , respectively. The strong correlations between pollutant concentrations and economic indicators show that the economic recession has resulted in proportionally lower levels of pollutants in large parts of Greece.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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