The regional impact of urban emissions on climate over central Europe: present and future emission perspectives
Abstrakt
The regional climate model RegCM4.2 was coupled to the chemistry transport model CAMx, including two-way interactions, to evaluate the regional impact of urban emission from central European cities on climate for present-day (2001-2010) and future (2046-2055) periods. Short-lived non-CO2 emissions are considered and, for the future impact, only the emission changes are accounted for (the climate is kept "fixed").
Two experiments are performed: one with all emissions included and one without urban emissions. The radiative impacts of non-CO2 primary and secondary pollutants are considered, ozone (O3), sulfates (PSO4), nitrates (PNO3), primary organic aerosol and elementary carbon (POA and PEC).
The impact on climate is characterized by significant cooling of up to -0.02 and -0.04 K in winter (DJF) and summer (JJA), mainly over cities. The main contributors to the cooling are the direct and indirect effects of the aerosols, while the ozone titration, plays rather a minor role.
In accordance with the vertical extent of the urban-emission-induced aerosol perturbation, cooling dominates the first few model layers up to about 150m in DJF and 1000m in JJA. We found a clear diurnal cycle of the radiative impacts with maximum cooling just after noon (JJA) or later in afternoon (DJF).
Furthermore, statistically significant decreases of surface radiation are modelled. The impact on the boundary layer height is small but statistically significant and decreases by 1 and 6m in DJF and JJA respectively.
We did not find any statistically significant impact on precipitation and wind speed. Regarding future emissions, the impacts are, in general, smaller as a consequence of smaller emissions, resulting in smaller urban-induced chemical perturbations.The study suggest that the non-CO2 emissions play rather a minor role in modulating regional climate over central Europe.
Much more important is the direct climate impact of urban surfaces via the urban canopy meteorological effects.