From global to regional scale: Impact of road traffic emissions on tropospheric ozone

Road traffic is an important source of anthropogenic emissions. Especially the emissions of nitrogen oxides (NOx), carbon monoxide (CO) and non-methane hydrocarbons (NMHC) are important, as they are precursors for the formation of ozone within the troposphere. This process of ozone formation is strongly non-linear. For example the efficiency of ozone formation depends strongly on the available amount of NOx. Therefore the amount of ozone production between rural and urban areas can differ significantly. But in current global chemistry-climate-models (CCM) with resolutions around 2° most urban areas can not be resolved explicitly, which may lead to a mixing of emissions from rural and urban areas within a grid box. Therefore an increased resolution of chemistry-climate-models is desirable to account for such regional effects. For this reason we investigate the impact of road traffic emissions with the MECO(n) model-system (MESSyfied ECHAM and COSMO models nested n-times). This model system couples the regional scale chemistry-climate system COSMO/MESSy (in one direction) with the global chemistry-climate system EMAC. This model-chain is as consistent as possible using the same atmospheric chemistry module MECCA and diagnostic methods on the global and regional scale. The coupling is done on-line allowing us to provide new boundary-conditions for dynamical and chemical fields every timestep of the global model. To quantify the effects of the road traffic emissions on the tropospheric ozone we use a detailed ozone diagnostic called "tagging" method. This method is an accounting system following the reaction pathways of the different species from the different sources, accounting for the nonlinearity of the chemistry. In addition also sensitivity experiments with different emissions databases (perturbation approach) are planned. Due to our consistent model chain we are able to compare directly our results on the global and the regional scale. Therefore we can quantify the effects of the horizontal resolution and analyze, if such increased resolutions are important for detailed ozone diagnostics. We present first results of our simulations focusing on the different effects on the global and the regional scale.