Abstract

There are multiple pathways urban areas impact environment: (i) cities represent intense emissions source of gaseous species and aerosols, having direct impact on the composition and chemistry of the atmosphere, (ii) certain gaseous and particulate material released and secondarily formed interact with radiation and cloud/rain microphysics, (iii) artificial urban surfaces represent additional sinks and sources of momentum, heat and moisture affecting the mechanical, thermodynamic and hydrological properties of local atmosphere and have specific impact on the meteorological conditions. An additional pathway of urban/meteorology/air-chemistry interaction arises from this third pathway: (iv) modified thermal and dynamic properties of urban air directly influence the transport, reactions and deposition of chemical species in urban air. Using regional climate chemistry modelling tool, we analysed the listed impacts/interactions over central Europe for the period of 2001-2010. We found, that the direct meteorological forcing of urban canopy is by more than one order larger than the impact on meteorology via radiative effects of the chemical changes introduced by urban emissions. In terms of temperature, urban surfaces lead to increase of day/night time values by up to 1.5 to 4°C, while the radiative effects are of order of 0.01 to 0.1°C and of opposite sign (due to urban aerosols). Regarding the impact on chemistry, the urban contribution to air pollution is significant not only over cities but over rural areas as well with contributions to the background pollution by a couple of 10%. Furthermore, we found that chemistry is largely modulated by the previously mentioned urban canopy meteorological effects - especially the urban induced turbulence enhancement and reduced wind have strong impact on transport of urban pollutants leading to significant modifications of the surface concentrations of both primary (NOx) and secondary pollutants (Ozone, HNO3).