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  • 1
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    The Indian Ocean experiment: widespread air pollution from South and Southeast Asia (2001)
    American Association for the Advancement of Science (AAAS)
    Details
    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
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    Aerosols, climate, and the hydrological cycle (2001)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2001-12-12
    Description: Human activities are releasing tiny particles (aerosols) into the atmosphere. These human-made aerosols enhance scattering and absorption of solar radiation. They also produce brighter clouds that are less efficient at releasing precipitation. These in turn lead to large reductions in the amount of solar irradiance reaching Earth's surface, a corresponding increase in solar heating of the atmosphere, changes in the atmospheric temperature structure, suppression of rainfall, and less efficient removal of pollutants. These aerosol effects can lead to a weaker hydrological cycle, which connects directly to availability and quality of fresh water, a major environmental issue of the 21st century.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ramanathan, V -- Crutzen, P J -- Kiehl, J T -- Rosenfeld, D -- New York, N.Y. -- Science. 2001 Dec 7;294(5549):2119-24.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Scripps Institution of Oceanography, University of California at San Diego, CA 92093, USA. ram@fiji.ucsd.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11739947" 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
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  • 3
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    Global air pollution crossroads over the Mediterranean (2002)
    American Association for the Advancement of Science (AAAS)
    Details
    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
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    The parasol effect on climate (2003)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2003-12-06
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Crutzen, Paul J -- Ramanathan, V -- New York, N.Y. -- Science. 2003 Dec 5;302(5651):1679-81; author reply 1679-81.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/14657476" 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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  • 5
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    The “anthropocene” (2002)
    EDP Sciences
    Details
    Publication Date: 2002-11-01
    Print ISSN: 1155-4339
    Electronic ISSN: 1764-7177
    Topics: Physics
    Published by EDP Sciences
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  • 6
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    Wavelength dependence of isotope fractionation in N2O photolysis (2003)
    Copernicus
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    Publication Date: 2003-03-21
    Description: In previous reports on isotopic fractionation in the ultraviolet photolysis of nitrous oxide (N2O) only enrichments of heavy isotopes in the remaining N2O fraction have been found. However, most direct photolysis experiments have been performed at wavelengths far from the absorption maximum at 182 nm. Here we present high-precision measurements of the 15N and 18O fractionation constants (ε) in photolysis at 185 nm. Small, but statistically robust depletions of heavy isotopes for the terminal atoms in the linear N2O molecule are found. This means that the absorption cross sections σ(15N 14N 16O) and σ(14N218O) are larger than σ(14N216O) at this specific wavelength. In contrast, the central N atom becomes enriched in 15N. The corresponding fractionation constants (±1 standard deviation) are 15ε1 = σ(15N 14N 16O)/σ(14N2 16O) - 1 = (3.7±0.2) %o 18ε = σ(14N218O)/σ(14N216O) - 1 = (4.5±0.2) %o  and 15ε2 = σ(14N 15N 16O)/σ(14N216O) - 1 = (-18.6±0.5) %o To our knowledge, this is the first documented case of such a heavy isotope depletion in the photolysis of N2O which supports theoretical models and pioneering vacuum ultraviolet spectroscopic measurements of 15N substituted N2O species that predict fluctuations of ε around zero in this spectral region (Selwyn and Johnston, 1981). Such a variability in isotopic fractionation could have consequences for atmospheric models of N2O isotopes since actinic flux varies also strongly over narrow wavelength regions between 175 and 200 nm due to the Schumann-Runge bands of oxygen. However, the spacing between maxima and minima of the fractionation constants and of the actinic flux differ by two orders of magnitude in the wavelength domain. The wavelength dependence of fractionation constants in N2O photolysis can thus be approximated by a linear fit with negligible consequences on the actual value of the spectrally averaged fractionation constant. In order to establish this linear fit, additional measurements at wavelengths other than 185 nm were made using broadband light sources, namely D2, Hg/Xe and Sb lamps. The latter lamp was used in conjunction with various interference filters to shift the peak photolysis rate to longer wavelengths. From these experiments and existing data in the literature, a comprehensive picture of the wavelength dependence of N2O photolysis near room-temperature is created.
    Print ISSN: 1680-7316
    Electronic ISSN: 1680-7324
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 7
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    Modeling the chemical effects of ship exhaust in the cloud-free marine boundary layer (2003)
    Copernicus
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    Publication Date: 2003-02-21
    Description: The chemical evolution of the exhaust plumes of ocean-going ships in the cloud-free marine boundary layer is examined with a box model. Dilution of the ship plume via entrainment of background air was treated as in studies of aircraft emissions and was found to be a very important process that significantly alters model results. We estimated the chemical lifetime (defined as the time when differences between plume and background air are reduced to 5% or less) of the exhaust plume of a single ship to be 2 days. Increased concentrations of NOx (= NO + NO2) in the plume air lead to higher catalytical photochemical production rates of O3 and also of OH. Due to increased OH concentrations in the plume, the lifetime of many species (especially NOx) is significantly reduced in plume air. The chemistry on background aerosols has a significant effect on gas phase chemistry in the ship plume, while partly soluble ship-produced aerosols are computed to only have a very small effect. Soot particles emitted by ships showed no effect on gas phase chemistry. Halogen species that are released from sea salt aerosols are slightly increased in plume air. In the early plume stages, however, the mixing ratio of BrO is decreased because it reacts rapidly with NO. To study the global effects of ship emissions we used a simple upscaling approach which suggested that the parameterization of ship emissions in global chemistry models as a constant source at the sea surface leads to an overestimation of the effects of ship emissions on O3 of about 50% and on OH of roughly a factor of 2. The differences are mainly caused by a strongly reduced lifetime (compared to background air) of NOxin the early stages of a ship plume.
    Print ISSN: 1680-7316
    Electronic ISSN: 1680-7324
    Topics: Geosciences
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  • 8
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    Inorganic bromine in the marine boundary layer: a critical review (2003)
    Copernicus
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    Publication Date: 2003-09-10
    Description: The cycling of inorganic bromine in the marine boundary layer (mbl) has received increased attention in recent years. Bromide, a constituent of sea water, is injected into the atmosphere in association with sea-salt aerosol by breaking waves on the ocean surface. Measurements reveal that supermicrometer sea-salt aerosol is substantially depleted in bromine (often exceeding 50%) relative to conservative tracers, whereas marine submicrometer aerosol is often enriched in bromine. Model calculations, laboratory studies, and field observations strongly suggest that the supermicrometer depletions reflect the chemical transformation of particulate bromide to reactive inorganic gases that influence the processing of ozone and other important constituents of marine air. Mechanisms for the submicrometer enrichments are not well understood. Currently available techniques cannot reliably quantify many Br containing compounds at ambient concentrations and, consequently, our understanding of inorganic Br cycling over the oceans and its global significance are uncertain. To provide a more coherent framework for future research, we have reviewed measurements in marine aerosol, the gas phase, and in rain. We also summarize sources and sinks, as well as model and laboratory studies of chemical transformations. The focus is on inorganic bromine over the open oceans outside the polar regions. The generation of sea-salt aerosol at the ocean surface is the major tropospheric source producing about 6.2 Tg/a of bromide. The transport of Br from continents (as mineral aerosol, and as products from biomass-burning and fossil-fuel combustion) can be of local importance. Transport of degradation products of long-lived Br containing compounds from the stratosphere and other sources contribute lesser amounts. Available evidence suggests that, following aerosol acidification, sea-salt bromide reacts to form Br2 and BrCl that volatilize to the gas phase and photolyze in daylight to produce atomic Br and Cl. Subsequent transformations can destroy tropospheric ozone, oxidize dimethylsulfide (DMS) and hydrocarbons in the gas phase and S(IV) in aerosol solutions, and thereby potentially influence climate. The diurnal cycle of gas-phase Br and the corresponding particulate Br deficits are correlated. Higher values of Br in the gas phase during daytime are consistent with expectations based on photochemistry. We expect that the importance of inorganic Br cycling will vary in the future as a function of both increasing acidification of the atmosphere (through anthropogenic emissions) and climate changes. The latter affects bromine cycling via meteorological factors including global wind fields (and the associated production of sea-salt aerosol), temperature, and relative humidity.
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    Electronic ISSN: 1680-7324
    Topics: Geosciences
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  • 9
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    Rarity of upper-tropospheric low O3 mixing ratio events during MOZAIC flights (2003)
    Copernicus
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    Publication Date: 2003-09-29
    Description: Only a few previous observations of very low O3 mixing ratios in the upper troposphere are available. The aim of this study was to examine the rich MOZAIC data set for more. Flights with at least 25 4 s averaged mixing ratios less than 8 ppbv at pressures lower than 500 hPa measured using commercial aircraft within the MOZAIC project have been analysed. There are eleven flights that fulfil these conditions (excluding artefacts as discussed below), representing about 0.001% of all measurements during the analysed period August 1994-December 1997. The low O3 events occurred over Southeast Asia, Africa, Brazil and the sea area 200 km east of Florida (US) and were all likely to be associated with transport of air masses from tropical sea areas. These low mixing ratio events occur in the upper troposphere during periods with generally low mixing ratios. They are not only found over sea, but also over land at pressure levels as low as 179 hPa. It could well be that some of the low O3 mixing ratio events measured during two or more flights belong to the same bigger low O3 mixing ratio area.
    Print ISSN: 1680-7316
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    Topics: Geosciences
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  • 10
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    A discussion on the determination of atmospheric OH and its trends (2003)
    Copernicus
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    Publication Date: 2003-02-07
    Description: The oxidation efficiency of the troposphere is largely determined by the hydroxyl radical and its global distribution. Its presence limits the lifetime of most trace gases. Because of the great importance of several of these gases for climate, ozone budget and OH itself, it is of fundamental importance to acquire knowledge about atmospheric OH and possible trends in its concentrations. In the past, average concentrations of OH and trends were largely derived using industrially produced CH3CCl3 as a chemical tracer. The analyses have given valuable, but also rather uncertain results. In this paper we describe an idealized computer aided tracer experiment which has as one of its goals to derive tracer concentration weighted, global average , where the temporal and spatial OH distribution is prescribed and k is the reaction rate coefficient of OH with a hitherto never produced (Gedanken) tracer, which is injected at a number of surface sites in the atmosphere in well known amounts over a given time period. Using a three-dimensional (3-D) time-dependent chemistry transport model, can be accurately determined from the calculated 3-D tracer distribution. It is next explored how well can be retrieved solely from tracer measurements at a limited number of surface sites. The results from this analysis are encouraging enough to actually think about the feasibility to carry out a global dedicated tracer experiment to derive and its temporal trends. However, before that, we propose to test the methods that are used to derive , so far largely using CH3CCl3, with an idealized tracer experiment, in which a global chemistry transport model is used to calculate the ``Gedanken'' tracer distribution, representing the real 3-D world, from which is derived, using only the tracer information from a limited set of surface sites. We propose here that research groups which are, or will be, involved in global average OH studies to participate in such an inter-comparison of methods, organized and over-seen by a committee appointed by the International Global Atmospheric Chemistry (IGAC) program.
    Print ISSN: 1680-7316
    Electronic ISSN: 1680-7324
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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