Ozone source attribution in polluted European areas during summer as simulated with MECO(n)

Abstract. Emissions of land transport and anthropogenic non-traffic emissions (e.g. industry, households and power generation) are significant sources of nitrogen oxides, carbon monoxide, and volatile organic compounds. These emissions are important precursors of tropospheric ozone and affect air quality. The contribution of emission sectors to ozone cannot be mea- sured directly, but calculated with sophisticated models of atmospheric chemistry only. For this study we apply a the MECO(n) model system (MESSy-fied ECHAM and COSMO models nested n times) equipped with a source attribution method to investigate the contribution of anthropogenic (land transport and non-traffic) and biogenic emissions to ozone in Europe. This model system couples a global chemistry-climate mode with a regional chemistry-climate model. Our source attribution (tag- ging) method fully decomposes the budgets of ozone and ozone precursors into contributions from various emission sources and regions. To estimate also the contributions of regional versus long-range transported contributions we distinguish four different source regions: Europe, North America, East Asia and Rest of the World. We performed one simulation covering 2 years with two regional refinements, one covering Europe (50 km resolution), and one covering Central Europe (12 km resolution). The model results are evaluated with data from European air quality stations and in situ data from the flight campaign Effect of Megacities on the Transport and Transformation of Pollutants on the Regional to Global Scales (EMeRGe) Europe in Summer 2017. Two study areas with large anthropogenic emissions, Benelux and Po Valley, are compared in detail. The absolute contributions of European land transport emissions to ground-level ozone for JJA 2017 in the Po Valley are larger than in the Benelux region (7 nmol mol⁻¹ and ≈ 3 nmol mol⁻¹), the same applies for the relative contributions with 12 % in the Po Valley and 7 % in the Benelux regions. Similar results are found for the contribution of European anthropogenic non-traffic emissions. Here, absolute contributions are larger in the Po Valley with 11 nmol mol⁻¹ (19 %) than 5 nmol mol⁻¹ (15 %) in the Benelux regions. The relative contributions to ozone from long-range transported land transport emissions in both regions in the range of 5–6 %, and the relative contributions from long-range transported non-traffic emissions are 9 % in the Po Valley and 13 % in the Benelux region. Contributions to ozone from long-range transported emissions are clearly more homogeneously distributed throughout Europe, whereas the distribution of contributions to ozone from European emissions is notably in-homogeneous. During periods of high ozone, contributions of European land transport and anthropogenic non-traffic emissions increase in particular over the Po Valley and in the Benelux. Especially in the Po Valley the increase is very strong and extreme ozone values could be mitigated in the Po Valley by reducing anthropogenic emissions.