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

Abstract

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

Impact of Static Urban Traffic Flow-Based Traffic Weighted Multi-Maps Routing Strategies on Pollutant Emissions

“…Pollutant emissions generated by urban traffic have noticeable impacts, mainly on air quality and health, greenhouse gas emissions, and the climate and weather conditions of the urban environment [3]. The main pollutants identified in the EMEP/EEA air pollutant emission inventory [4] are:…”

Birds differentially prioritize visual and olfactory foraging cues depending on habitat of origin and sex

“…The behaviour of urban birds is influenced by anthropogenic noise and light, with negative fitness consequences; these sensory pollutants have also been linked to bird signalling and sensory perception [ 11 ]. In addition, urban areas contain high levels of volatile chemicals [ 14 ] that may act as olfactory sensory pollutants, but possible effects of anthropogenic odours on birds have not been studied.…”

Impact of urbanization on fine particulate matter concentrations over central Europe

“…The RUT acts via two primary pathways: a) with the human activities concentrated in urban areas great amount of emissions are introduced (both green-house-gas and short-lived pollutants) which affect the local but also the regional and global air pollution (Im and Kanakidou, 2012;Markakis et al, 2015;Timothy and Lawrence, 2009;Butler and Lawrence, 2009;Stock et al, 2013;Huszar et al, 2021), b) urban land-surface differs greatly from rural one by introducing artificial object and surfaces with specific geometries (e.g. street canyons, buildings) which affect the surface-air fluxes of energy, momentum and material with strong consequences on meteorological conditions (Oke, 1982;Oke et al, 2017;Karlický et al, 2020) and at the same time, in long-term, they modify the regional climate (Huszar et al, 2014;Karlický et al, 2018).…”

“…Regarding the first pathway, it is clear that urban emissions alone substantially deteriorate the local air-pollution (Thunis et al, 2021). They are composed with a mixture of different gases like oxides of nitrogen (NOx) originating mainly from road transportation (Huszar et al, 2016a(Huszar et al, , 2021 along with the volatile organic compounds (VOC), carbon monoxide (CO) and sulphur dioxide (SO 2 ) or ammonia (NH 3 ). Further, urban emissions contain also primary aerosol in the form of elemental carbon (PEC), primary organic aerosol (POA) and other primary material like metals (Freney et al, 2014;Allan et al, 2010;Rivellini et al, 2020;Yang et al, 2023).…”

“…However, on the other hand, secondary pollutant like ozone can respond differently and for these cities often decreases in urban cores are modelled due to high NOx-to-VOC ratio (e.g. Huszar et al, 2016aHuszar et al, , 2021. Further, it was found that air pollution in cities is determined mainly by the local sources, however a considerable part of the total concentration is associated to rural ones (Panagi et al, 2020;Thunis et al, 2021;Huszar et al, 2021).…”