Atmos. Chem. Phys. Discuss., 5, 10339-10367, 2005
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Global impact of road traffic emissions on tropospheric ozone
S. Matthes1, V. Grewe1, R. Sausen1, and G.-J. Roelofs2
1Institut für Physik der Atmosphäre, DLR-Oberpfaffenhofen, Wessling, Germany
2Institut for Marine Research, University of Utrecht, Utrecht, The Netherlands

Abstract. Road traffic is one of the major anthropogenic emission sectors for NOx, CO and NMHCs (non-methane hydrocarbons). We applied ECHAM4/CBM, a general circulation model coupled to a chemistry module, which includes higher hydrocarbons, to investigate the global impact of road traffic emissions on the atmosphere. Improving over previous global modelling studies, which concentrated on road traffic NOx and CO-emissions only, we assess the impact of NMHC-emissions from road traffic. It is revealed that NMHC-emissions from road traffic play a key role for the impact on ozone. They are responsible for (indirect) long-range transport of NOx from road traffic via the formation of PAN, which is not found in a simulation without NMHC emissions from road traffic. Long-range transport of NMHC-induced PAN impacts on the ozone distribution in northern hemisphere regions far away from the sources, especially in Arctic and remote maritime regions. There, during subsidence, PAN acts as a source for NOx, caused by thermal decay. Hence, ozone is produced. In July total road traffic emissions (NOx, CO and NMHCs) contribute to the zonally averaged ozone distribution by more than 12% near the surface in the northern hemisphere midlatitudes and arctic latitudes. In January road traffic emissions contribute near the surface in northern and southern extratropics more than 8%. Sensitivity studies for regional emission show that effective transport of road traffic emissions occurs mainly in the free troposphere. In tropical latitudes of America up to an altitude of 200 hPa, global road traffic emissions contribute about 4% to the ozone concentration.

Citation: Matthes, S., Grewe, V., Sausen, R., and Roelofs, G.-J.: Global impact of road traffic emissions on tropospheric ozone, Atmos. Chem. Phys. Discuss., 5, 10339-10367, doi:10.5194/acpd-5-10339-2005, 2005.
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