The regional impact of urban emissions on air quality in Europe: the role of the urban canopy effects

Abstract. Urban areas are hot spots of intense emissions, and they influence air quality not only locally but on a regional or even global scale. The impact urban emissions over different scales depends the dilution chemical transformation plumes which governed by local- regional-scale meteorological conditions. These influenced presence urbanized land surface via so-called canopy forcing (UCMF). In this study, we investigate for selected central European cities (Berlin, Budapest, Munich, Prague, Vienna Warsaw) how emission (UEI) is modulated UCMF present-day climate conditions (2015–2016) using two models, models RegCM Weather Research Forecasting model coupled with Chemistry (WRF-Chem; its part), chemistry transport Comprehensive Air Quality Model Extensions (CAMx) to either WRF “chemical” component WRF-Chem. was calculated replacing rural one, while UEI estimated removing all anthropogenic from cities. We analyzed urban-emission-induced changes in near-surface concentrations NO2, O3 PM2.5. found increases NO2 PM2.5 4–6 ppbv µg m?3, respectively, meaning that about 40 %–60 % 20 %–40 caused local rest result surrounding areas. showed if included, these pollutants smaller, other words, overestimated effects taken into account. case ozone, due usually predict decreases around ?2 ?4 (about 10 %–20 %), again smaller considered (by 60 %). further extreme (95th percentile) pollution much stronger, modulation also larger such situations. Finally, evaluated contribution urbanization-induced modifications vertical eddy diffusion it alone able explain modeled decrease considered. summary, our results resulting urbanization have be included studies intend quantify footprint emissions. Ignoring can lead strong overestimation UEI.