Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 5 2005 10.5194/acpd-5-10339-2005 http://www.atmos-chem-phys-discuss.net/5/10339/2005/ http://www.atmos-chem-phys-discuss.net/5/10339/2005/acpd-5-10339-2005.html http://www.atmos-chem-phys-discuss.net/5/10339/2005/acpd-5-10339-2005.pdf 10339 10367 2005-10-24 Global impact of road traffic emissions on tropospheric ozone S. Matthes V. Grewe R. Sausen G.-J. Roelofs Institut für Physik der Atmosphäre, DLR-Oberpfaffenhofen, Wessling, Germany Institut for Marine Research, University of Utrecht, Utrecht, The Netherlands Road traffic is one of the major anthropogenic emission sectors for NO<sub>x</sub>, 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 NO<sub>x</sub> 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 NO<sub>x</sub> 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 NO<sub>x</sub>, caused by thermal decay. Hence, ozone is produced. In July total road traffic emissions (NO<sub>x</sub>, 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&nbsp;hPa, global road traffic emissions contribute about 4% to the ozone concentration.