Impact of road traffic emissions on tropospheric ozone

Abstract

Emissions from road traffic are important anthropogenic sources of carbon monoxide (CO), nitrogen oxide (NOx) and non-methane hydrocarbons (NMHCs). In a complex nonlinear chemical mechanism these substances act as precursor for tropospheric ozone. Despite this nonlinear chemistry the sensitivity of the ozone production from road traffic emissions is often studied using the perturbation approach. In this approach the chemical system is linearized around a reference simulation. This method is well suited while studying the impacts of emission policies, but it can cause misinterpretations while evaluating the attribution of different sources on chemical species. For such questions the “tagging” method is well suited which is an accounting system following the reaction pathways of the different species from different sources, allowing to study the nonlinear behavior of the chemical system. Therefore we are using this tagging method to evaluate the impact of road traffic emissions on the tropospheric ozone and further compare these results with sensitivity studies.

A tagging method has been integrated into the MECO(n) modelsystem (MESSyfied ECHAM and COSMO models nested n-times) which couples the regional scale chemistry-climate system COSMO/MESSy (in one direction) with the global chemistry-climate System EMAC. In contrast to the popular off-line coupling MECO(n) uses an on-line coupling allowing us to couple not only the dynamical variables but also the chemical variables in every time step of the global model. This model chain enables us to be (with respect to diagnostic methods and the boundary conditions) as consistent as possible from the global to the local scale and to evaluate the impact of the lateral resolution on detailed ozone-chemistry diagnostics like the tagging method.

We present first results comparing simulations using the “perturbation approach” with the results from the tagging method focusing on the impact of road traffic emissions in Europe from global to local scale.