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Preprints
https://doi.org/10.5194/acp-2020-399
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-399
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 24 Jun 2020

Submitted as: research article | 24 Jun 2020

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This preprint is currently under review for the journal ACP.

The impact of urban land-surface on extreme air pollution over central Europe

Peter Huszar1, Jan Karlický1,3, Jana Ďoubalová1,2, Tereza Nováková1, Kateřina Šindelářová1, Filip Švábik1, Michal Belda1, Tomáš Halenka1, and Michal Žák1 Peter Huszar et al.
  • 1Department of Atmospheric Physics, Faculty of Mathematics and Physics, Charles University, Prague, V Holešovičkách 2, 180 00 Prague 8, Czech Republic
  • 2Czech Hydrometeorological Institute (CHMI), Na Šabatce 17, 14306, Prague 4, Czech Republic
  • 3Institute of Meteorology and Climatology, Department of Water, Atmosphere and Environment, University of Natural Resources and Life Sciences, Vienna, Gregor-Mendel-Straße 33, 1180 Vienna, Austria

Abstract. This paper deals with the urban land-surface impact (i.e. the urban canopy meteorological forcing; UCMF) on extreme air pollution for selected central European cities for present-day climate conditions (2015–2016) using three regional climate-chemistry models: the regional climate models RegCM and WRF-Chem (its meteorological part), the chemistry transport model CAMx coupled to either RegCM and WRF and the chemical component of WRF-Chem. Most of the studies focused on the change of average conditions or only on a selected winter and summer air pollution episode. Here we extend these studies by focusing on long term extreme air pollution levels by looking at not only the change of average values but also their high (and low) percentile values and we combine the analysis with investigating selected high pollution episodes too. As extreme air pollution is often linked to extreme values of meteorological variables (e.g. low planetary boundary layer height, low winds, high temperatures), the extreme meteorological modifications will be analyzed too. The validation of model results shows reasonable model performance for regional scale temperature and precipitation. Ozone is overestimated by about 10–20 μg m−3, on the other hand, extreme summertime ozone values are underestimated by all models. Modeled nitrogen dioxide (NO2) concentrations are well correlated with observations, but results are marked with a systematic underestimation up to 20 μg m−3. PM2.5 (particles with diameter < 2.5 μg m−3) are systematically underestimated in most of the models by around 5 μg m−3.

Our results show that the impact on extreme values of meteorological variables can be substantially different from that of the impact on average ones: low (5 % percentile) temperature in winter responds to UCMF much more than average values, while in summer, 95 % percentiles increase more than averages. The impact on boundary layer height (PBLH), i.e. its increase is stronger for thicker PBLs and wind-speed is reduced much more for strong winds compared to average ones. The modeled changes of ozone (O3), NO2 and PM2.5 show the expected pattern, i.e. increase in average 8-hour O3 up to 2–3 ppbv, decrease of daily average NO2 by around 2–4 ppbv and decrease of daily average PM2.5 by around −2 μg m−3. Regarding the impact on extreme (95 % percentile) values of these pollutants, the impact on ozone at the high-end of the distribution is rather similar to the impact on average 8-hour values. A different picture is obtained however for extreme values of NO2 and PM2.5. The impact on the 95 % values is almost 2 times larger than the impact on the daily averages for both pollutants. The simulated impact on extreme values further well corresponds to the UCMF impact simulated for the selected high pollution episodes. Our results bring light to the principal question: whether extreme air quality is modified by urban land-surface with a different magnitude compared to the impact on average air pollution. We showed that this is indeed true for NO2 and PM2.5 while in case of ozone, our results did not show substantial differences between the impact on mean and extreme values.

Peter Huszar et al.

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Short summary
The paper shows how extreme meteorological conditions change due to the urban land-cover forcing and how this translates to the impact on the extreme air pollution over central European cities. It focuses on ozone, nitrogen dioxide, and particulate matter with a diameter of less than 2.5 μm and shows that while for the extreme daily maximum 8-hour ozone, changes are same as for the mean ones, a much stronger increase is calculated for extreme NO2 and PM2.5 compared to their mean changes.
The paper shows how extreme meteorological conditions change due to the urban land-cover forcing...
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