The Impact of Urban Emissions on Chemistry and Climate over Central Europe

Abstract:

The impact of city emissions of short lived gases and aerosols on the tropospheric chemistry and climate is examined over Central Europe. A coupled modelling system consisting of the regional climate model RegCM4 and the chemistry transport model CAMx is implemented over a 10 km x 10 km resolution domain. For each period of 2001-2010, 2026-2035 and 2046-2055 a pair of experiments is performed: one with urban emissions removed and one with urban emissions scaled by the factor. The chemistry-climate impact is evaluated as the difference between the corresponding experiments divided by this factor. This choice was important to obtain statistically significant results. The linearity is examined to justify this approach. The radiative feedbacks of tropospheric ozone, primary (black and organic carbon) and secondary inorganic aerosols (sulfates and nitrates) are taken into account including the 1st and 2nd indirect aerosol effect. Due to city emissions, we found significant ozone titration especially over the western and northern part of the domain. City emissions contribute to ozone production over southern Europe. An increase of sulfate, nitrate aerosols and black/organic is significant as well and is modelled not only over urbanized areas but all over the computational domain. Evaluating the radiative impacts, we found that the total urban impact on 2 m temperature over central Europe is characterized by cooling up to -0.015 K as a 2001-2010 average. The radiative impact of the individual constituents (ozone, sulfate-, nitrate aerosols etc.) is examined as well.