We considered Moscow-specific features of time variations in PM2.5mass concentration in the surface air layer as a function of a number of atmospheric parameters such as the concentrations of...

During 2020–2021, a comprehensive experiment was conducted to study the composition of near-surface atmospheric aerosol in Moscow. The paper considers the experimental data together with synoptic and meteorological conditions. Attention is focused on six episodes of extremely high aerosol mass concentration values: in March and October 2020, as well in March, April, May and July 2021. In all these cases (and only in them), the average daily mass concentration of PM₁₀ aerosol exceeded the Maximum Permissible Concentration (MPC) value (according to Russian standards, 60 μg/m³). The origin of the aerosol during these periods of extreme pollution is revealed, which is the main result of the work. It was shown that the July episode of 2021 was associated with a local intensive anthropogenic source that arose as a result of the active dismantling and demolition of multistory industrial buildings. The remaining spring and autumn episodes were caused by atmospheric transport of both smoke aerosol from various regions with strong biomass fires and dust aerosol from arid zones of the south of European territory of Russia (ETR) with dust wind storms. The cases of atmospheric pollution transport to Moscow region from the other regions are confirmed with the help of air mass transport trajectories (HYSPLIT 4 model) and MERRA-2 reanalysis data on black carbon and/or dust distribution in the atmosphere over ETR. Differences in the elemental composition of the near-surface aerosol of Moscow air during periods with extremely high aerosol concentrations are analyzed in comparison with each other and with unperturbed conditions for the season.

The results of an intensive complex experiment carried out from March 25 to May 3, 2020, to study the composition and time variability of urban aerosol in the atmosphere in the center of Moscow include data on daily mean concentrations of both РМ₁₀ and РМ_2.5 particles and 65 chemical elements. The concentrations of all components did not exceed the maximum permissible concentration (MPC) for residential areas. The exception was increased РМ₁₀ concentrations recorded on March 27–29, when air masses from neighboring regions with biomass fires arrived in the city. The coefficients of correlation between values of the concentrations and enrichment factors of the elements confirmed the anthropogenic/local origin of some heavy metals (Cd, Sb, Pb, Se, Th) and the terrigenous/global origin of elements such as Mn, Mg, Zn, Co, Fe, Al, and Cr. The elements S, P, K, Na, Ca, Ni, Cu, Mo, Sn, W, Bi, and U, for which no significant correlation between their concentrations and enrichment factors has been found, apparently, have a mixed origin from both natural and anthropogenic sources competing with each other from day to day. The first studies of the weekly cycle of the relative elemental composition of surface aerosol in Moscow have shown the leading role of meteorological conditions (in particular, air pressure and humidity) in variations of aerosol pollution levels.

The influence of aerosols on various hydrometeorological processes was discussed.

The seasonal changes in the elemental composition of surface aerosol in Moscow are considered in four data series: for summer and autumn 2019 and winter and spring 2020. The surface aerosol is significantly enriched with sulfur, heavy metals, and metalloids (Cu, Zn, Cd, Sb, Pb, Bi, etc.). The mass concentrations, mass percentages, and enrichment factors for different elements in aerosol particles are determined and compared for different seasons. The spatial distribution of elements in surface aerosol is not uniform through the city, which may be associated with the specificity of local sources, underlying surface, and wind regime in different regions of Moscow. The highest concentrations of a number of terrigenous and anthropogenic elements are revealed in the Central Administrative District of Moscow. The causes for seasonal variability in the elemental composition of surface aerosol in the Moscow megalopolis and possible sources of elements are discussed.

We analyzed the unique episode of long-range dust/sand atmospheric aerosol transport from the arid zones of the southern European territory of Russia, i.e. the Northern Caspian and Astrakhan regions and the Kalmykia Republic, to the Moscow region during fall 2020. Intensive complex experiments were carried out at the A.M. Obukhov Institute of Atmospheric Physics of the Russian Academy of Sciencesin the center of Moscow through different seasons during 2020–2021 to study the composition of near-surface aerosols in the Moscow megacity. The experimental data are considered to take into account the synoptic features and meteorological conditions. Abnormally high values of near-surface aerosol mass concentrations in Moscow were registered during the period from 6 to 14 of October 2020 under stable anti-cyclonic conditions, with calm or quiet/light wind (1–2 m/s), and under the conditions of the dominance of southeastern air mass transport. At the same time, the average daily mass concentration of aerosol particles PM₁₀ exceeded the Maximum Permissible Concentration (MPC) value (60 µg/m³) by 1.5–4.5 times, and the number of large (micron) particles increased by an order or more. Comparative analysis of aerosol elemental composition in Moscow (during this episode) and in Kalmykia (according to observations in July 2020) showed high correlation for terrigenous elements' patterns. The aerosol origin for this episode was confirmed by performing long-range trajectory analysis of air mass transport (HYSPLIT model), and by using MERRA-2 reanalysis data for dust aerosol spatial distribution.