Modeling the drivers of fine PM pollution over Central Europe: impacts and contributions of emissions from different sources

Abstract. Air pollution nowadays represents the most significant environmental health risk in Europe, with fine particulate matter (PM_2.5) being among the pollutants with the most critical threat to the human health, especially in urban areas. Identifying and quantifying the sources of PM_2.5 components are essential prerequisites for designing effective strategies to mitigate this kind of air pollution. In this study, we utilized the numerical weather prediction model WRF (Weather Research and Forecast Model) coupled with the chemistry transport model CAMx (Comprehensive Air quality Model with Extensions) to investigate the relationships between emissions (with a primary focus on emissions covering a wide range of anthropogenic activities) and the concentrations of total PM_2.5 and its secondary components (ammonium, nitrate, sulfate, and secondary organic aerosol (SOA)) in the region of Central Europe (with a more detailed focus on six large cities in this region, namely Berlin, Munich, Vienna, Prague, Budapest, and Warsaw) during the period 2018–2019 using the PSAT (Particulate Source Apportionment Technology) tool implemented in CAMx and the zero-out method (an extreme case of the brute-force method), which makes this study, taking into account the differentiation of individual GNFR sectors of anthropogenic activity, the only one of its kind for this region.

The use of the PSAT tool showed, among other things, that during the winter seasons, emissions from other stationary combustion (including residential combustion), boundary conditions, road transport, and agriculture-livestock contribute most extensively to the average PM_2.5 concentrations (their domain-wide average contributions are 3.2, 2.1, 1.4, and 0.9 μg m^-3, respectively), while during the summer seasons, the average PM_2.5 concentrations are mainly contributed by biogenic emissions, followed by emissions from road transport, industrial sources, and boundary conditions (their domain-wide average contributions are 0.57, 0.31, 0.28, and 0.27 μg m^-3, respectively). In contrast, the most considerable average seasonal impacts on the concentration of PM_2.5 when modeling with the SOAP mechanism activated (i.e., with the same SOA formation mechanism that is implemented when using the PSAT tool; we named this sensitivity experiment as the SOAP experiment) are caused by the overall reduction of emissions from other stationary combustion, agriculture-livestock, road transport, and agriculture-other during the winter seasons (their domain-wide averages are 3.4, 2.9, 1.4, and 1.1 μg m^-3, respectively), while during the summer seasons, they are induced by emissions from agriculture-livestock, road transport, industrial sources, and other stationary combustion (0.46, 0.45, 0.34, and 0.29 μg m^-3, respectively).

Further, we revealed that the differences between the contributions of emissions from anthropogenic sectors to PM_2.5 concentration and the impacts of these emissions on PM_2.5 concentration in the SOAP experiment are predominantly caused by the secondary aerosol components (due to the acting of oxidation-limiting and/or indirect effects). Moreover, the most substantial of these differences, in terms of daily averages in the cities (reaching up to ≈15 μg m^-3 in some of them during winter time) and seasonal averages for the winter and summer seasons (reaching up to 4.5 and 1.25 μg m^-3, respectively), are associated with emissions from agriculture-livestock, mainly due to differences in nitrate concentrations.

Finally, we performed one more sensitivity experiment (named the VBS experiment) based on the zero-out method, in which gas-aerosol partitioning and chemical aging of organic aerosol were activated using the 1.5-D VBS scheme, and we also added the estimates of intermediate-volatility and semivolatile organic compounds. We found that their application, in comparison with the results of the SOAP experiment, mainly increases the average seasonal impacts on the concentration of PM_2.5 caused by the overall reduction of emissions from other stationary combustion and road transport during the winter seasons (the increases reach up to 12 and 4 μg m^-3, respectively) and mainly by increasing the average seasonal impact on the concentration of PM_2.5 produced by the overall reduction of emissions from road transport during the summer seasons (the increase reach up to 2.25 μg m^-3).