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This article summarizes the data of the chemical composition and the acidity of the seasonal snow precipitation for the cold periods 1999-2006 (n=180), 2010-2013 (n=82) and 2018-2019 (n=18) in different parts of Moscow. Major ions content was measured, such as SO42-, НСO3-, Cl-, NO3-, Са2+, Mg2+, Na+, K+ and NH4+, also pH and sum of ions (mg/L) were measured. During the 2018-2019 season, snowpack samples were taken twice at 4 sites in Moscow: two in the North-East Administrative Okrug (NEAO) near the road and in the park at the distance of 3 km from each other, and two in the South- Western Administrative Okrug (SWAO) and in the Western Administrative Okrug (WAO) near the road and in the park at the distance of 6 km from each other. Samples were taken with a break of 5 days to determine the dynamics of the chemical composition within the beginning of the snow-melting. In each pair of sampling sites there was one that is located in the park and one located near the road. This experiment showed a slight variability of the chemical composition of snow during 5 days under the influence of the new snowfall. In general, there is a trend of changing the composition of snow from calcium carbonate to calcium chloride, which is mainly connected to the use of anti-icing reagents; for the same reason, the areas that are closer to the roads are the most polluted.

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The monograph is devoted to the study of atmospheric aerosol and its dynamics in the urban environment of Moscow megacity. Based on the AeroRadCity 2018-2019 complex experiment, composed of measurement campaign and numerical experiments using the COSMO-ART chemical transport model, a number of new results were obtained, which contributed to a deeper understanding of the gas-aerosol composition of the urban atmosphere, wet aerosol deposition with accounting of geochemical processes and aerosol radiative effects. Aerosol pollution in the Moscow region and its dynamics in the 21st century were estimated according to the aerosol retrievals using the MAIAC algorithm developed for the MODIS satellite instrument, and long-term AERONET measurements. The effects of aerosol on meteorological and radiative characteristics of the atmosphere were obtained from the numerical experiments with the COSMO model and long-term observations. The indirect aerosol effects on cloud characteristics and weather forecast were estimated.

For the first time, the wet deposition and washout rates of soluble forms of potentially toxic elements (PTEs) were estimated in rains during the spring AeroRadCity experiment in Moscow. Rains are an important factor in reducing atmospheric pollution with PTEs in Moscow. Due to the resuspension of contaminated particles of road dust and urban soils, industrial and traffic impact, waste and biomass burning, rainwater is highly enriched in Sb, Pb, Se, Cd, and S, and less enriched in P, Ba, As, W, Mn, Sn, Na, Co, Ni, and Be. Significant wet deposition (μg/m2 per event) and washout rates (μg/m2 per hour) of PTEs were revealed during the public holidays in May which corresponded to the elevated aerosol content due to predominant air advection from southern and south-western regions in this period. During continuous rains, the level of PTEs wet deposition sharply decreases on the second and subsequent days due to the active below-cloud washout of aerosols during the initial precipitation events. We show that the length of the dry period and aerosol content before the onset of rain determines the amount of solid particles in rainwater, which leads to an increase in rainwater pH, and strongly affects wet deposition and washout rates of PTEs of mainly anthropogenic origin (W, Zn, Bi, Cd, Sb, Ni, B, S, K, and Cu). At the same time rainfall intensity contributes to an increase in wet deposition and washout rates of Se, As, B, Cu, Sb, S, Cd, Ba, Rb, and K. The obtained results provide a better understanding of atmospheric deposition processes and can be useful in assessing the urban environmental quality.

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