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          Institute: MPI für Meteorologie     Collection: Atmosphere in the Earth System     Display Documents

ID: 256389.0, MPI für Meteorologie / Atmosphere in the Earth System
Assessment of the global impact of aerosols on tropospheric oxidants
Authors:Tie, X. X.; Madronich, S.; Walters, S.; Edwards, D. P.; Ginoux, P.; Mahowald, N.; Zhang, R. Y.; Lou, C.; Brasseur, G.
Date of Publication (YYYY-MM-DD):2005-02-10
Title of Journal:Journal of Geophysical Research-Atmospheres
Journal Abbrev.:J. Geophys. Res.-Atmos.
Issue / Number:D3
Sequence Number of Article:D03204
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:We present here a fully coupled global aerosol and chemistry model for the troposphere. The model is used to assess the interactions between aerosols and chemical oxidants in the troposphere, including (1) the conversion from gas-phase oxidants into the condensed phase during the formation of aerosols, (2) the heterogeneous reactions occurring on the surface of aerosols, and (3) the effect of aerosols on ultraviolet radiation and photolysis rates. The present study uses the global three-dimensional chemical/transport model, Model for Ozone and Related Chemical Tracers, version 2 (MOZART-2), in which aerosols are coupled with the model. The model accounts for the presence of sulfate, soot, primary organic carbon, ammonium nitrate, secondary organic carbon, sea salt, and mineral dust particles. The simulated global distributions of the aerosols are analyzed and evaluated using satellite measurements (Moderate-Resolution Imaging Spectroradiometer (MODIS)) and surface measurements. The results suggest that in northern continental regions the tropospheric aerosol loading is highest in Europe, North America, and east Asia. Sulfate, organic carbon, black carbon, and ammonium nitrate are major contributions for the high aerosol loading in these regions. Aerosol loading is also high in the Amazon and in Africa. In these areas the aerosols consist primarily of organic carbon and black carbon. Over the southern high-latitude ocean (around 60°S), high concentrations of sea-salt aerosol are predicted. The concentration of mineral dust is highest over the Sahara and, as a result of transport, spread out into adjacent regions. The model and MODIS show similar geographical distributions of aerosol particles. However, the model overestimates the sulfate and carbonaceous aerosol in the eastern United States, Europe, and east Asia. In the region where aerosol loading is high, aerosols have important impacts on tropospheric ozone and other oxidants. The model suggests that heterogeneous reactions of HO₂ and CH₂O on sulfate have an important impact on HOx (OH + HO₂) concentrations, while the heterogeneous reaction of O₃ on soot has a minor effect on O₃ concentrations in the lower troposphere. The heterogeneous reactions on dust have very important impacts on HOx and O₃ in the region of dust mobilization, where the reduction of HOx and O₃ concentrations can reach a maximum of 30% and 20%, respectively, over the Sahara desert. Dust, organic carbon, black carbon, and sulfate aerosols have important impacts on photolysis rates. For example, the photodissociation frequencies of ozone and nitrogen dioxide are reduced by 20% at the surface in the Sahara, in the Amazon, and in eastern Asia, leading to 5–20% reduction in the concentration of HOx and to a few percent change in the O₃ abundance in these regions.
Free Keywords:aerosols, troposphere, oxidants.
External Publication Status:published
Document Type:Article
Communicated by:Carola Kauhs
Affiliations:MPI für Meteorologie/Atmosphere in the Earth System
External Affiliations:Natl Ctr Atmospher Res, Boulder, CO 80305 USA.; NOAA, Geophys Fluid Dynam Lab, Princeton, NJ 08542 USA.; Texas A&M Univ, Dept Atmospher Sci, College Stn, TX 77843 USA.; Univ Calif Santa Barbara, Inst Computat Earth Syst Sci, Santa Barbara, CA 93106 USA
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