Study of the variability of physicochemical characteristics of surface aerosol in Moscow under atypical weather conditions in 2019

In recent years, interest in studying the physicochemical parameters of atmospheric aerosols, which is associated with their active influence on the air pollution, optical characteristics of the atmosphere and the Earth’s climate has increased. Climatic changes cause the occurrence of atypical weather conditions and dangerous meteorological phenomena that affect changes in the properties of aerosol particles. In large industrial megacities frequent atypical meteorological situations change aerosols behavior and complicate the predictive model assessment of the air quality and thermal regime of the atmosphere.

We consider the results of studies of the daily and seasonal variability of the chemical composition, microphysical parameters, and mass concentration of surface aerosols in Moscow under atypical weather conditions prevailing in summer (June 10-July 10) and in autumn (October 10-November 7) of 2019. In the second half of June 2019, strong cyclonic activity was observed, and air masses of Arctic origin dominated, bringing intense rainfall, cleansing the atmosphere of contaminants and significant decrease in air temperature. October was characterized by air temperature above the climatic norm, insignificant precipitation and frequent strong gusts of wind of western direction.

Under such conditions, abnormally low aerosol PM_2.5 and PM₁₀ concentrations were found, and in the summer average monthly concentrations were 1.5 times lower than in the autumn period what is untypical for aerosols. Usually aerosols annual course is characterized by broad maximum in summer, and by minimum in October-November. In addition, comparison with the results of observations of previous years showed that in 2019 aerosol concentration was 3-5 times lower during both summer and autumn. In particular, the average monthly calculated concentration of  submicron fraction in the study period was: 273 particles/cm³ in the summer and 405 particles/cm³ in the autumn; mass concentration of PM_2.5 particles: 3.9 and 5.4 μg/m³, respectively. For comparison, multiyear average mass concentrations of PM_2.5 are 15-30 μg/m³. The day-to-day variability and weekly cyclicity of atmospheric aerosols also underwent changes as a result of synoptic and meteorological factors. Under these conditions, the contribution of urban anthropogenic sources, including traffic leveled, in particular, due to such intensive processes as leaching and weathering of aerosols from the atmosphere.

Simultaneously with the measurement of microphysical parameters, the elemental composition of aerosol samples was determined by inductively coupled plasma mass spectrometry. It showed that atmospheric aerosol particles are characterized by a high content of sulfur, heavy metals (Cd, Cu, Zn, Mo, W, Ti, Au, Hg, Pb, Ag, Mn, Fe, Co, As), and metalloids (Bi, Sb, B, P, As, Sn), mainly of anthropogenic nature. Such harmful substances are accumulated in the fine fractions of particles that are part of the PM_2.5 aerosol and most dangerous for human health.

Large amplitudes of variations in the disperse composition and concentration of aerosol particles in the atmospheric surface layer, recorded during seasonal observations under atypical weather conditions, characterize strong inhomogeneities of aerosol parameters in space and time, which can significantly affect the chemical and optical properties of aerosols, as well as lower atmosphere state in general.

The reported study was funded by RFBR, projects ## 05-19-00352 and 05-19-50088.