Variability of atmospheric aerosol element composition in Moscow in 2019 and 2020

The data of intensive complex experiment carried out by A.M. Obukhov Institute of Atmospheric Physics RAS to study the atmospheric composition in Moscow gave some new results on seasonal and daily variations in the elemental composition of surface aerosol in Moscow. The elemental composition of daily aerosol samples includes 65 chemical elements from Li to U, measured by ICPM spectrometer (during about 40 days in each of four seasons from summer 2019 to spring 2020). The enrichment factors (EFs) of element concentrations in relation to earth’s crust allowed us to distinguish terrigenous (Mn, Mg, Zn, Fe, Al, etc.) and anthropogenic (for example, Cd, Sb, Pb) elements.

The correlations between temporal variations in element concentrations and EFs helped us to divide all elements into 4 groups: elements of global distribution, heavy metals and metalloids of predominantly terrigenous or anthropogenic origin, radioactive elements. Heavy metals and sulfur, the main sources of which in Moscow are engines, are the elements of anthropogenic/local origin. In winter and summer seasons, the EFs of the most of these elements reach their highest values, which indicates an increase of anthropogenic emissions (heating and energetics, road transport) in cold season and soil/dust contributions in summer. Elements of terrigenous/global origin have small seasonal variations in EFs. In winter, coefficients of aerosol accumulation for a number of anthropogenic elements are high because of the low values of their deposition rates onto the cold or also snow-covered surface.

The spatial distribution of anthropogenic/local origin elements in surface aerosol in Moscow is not uniform, which is associated with the specificity of the sources, the features of the underlying surfaces and the wind regimes in different regions of the metropolis. The maximal ​​element concentrations are in the central region of the city, in densely built-up areas and near highways with high traffic loads.

Meteorological and synoptic conditions have a strong influence on the composition of the surface aerosol and its variability in Moscow. In the spring of 2020, weekly cycle of element concentrations corresponded to weather parameters. Under anticyclonic conditions, aerosol particles accumulate in the surface layer of the atmosphere. With pressure drop and humidity increase, cleaning of the atmosphere from aerosol particles occurs by washout with precipitation or by coagulation and deposition onto the surface.

We tried to identify in Moscow aerosol element composition any specific features due to the restrictive measures to prevent the spread of coronavirus infection from 26 March 2020. On the one hand, during the lockdown, there is a decrease in anthropogenic (especially transport) emissions to the city atmosphere. On the other hand, a number of chemical elements should be added into the environment during the disinfection of soils and streets. So far, insufficient data does not allow us to make any determined conclusions. To detect defined changes in aerosol composition, it is necessary to compare with measurement data in other seasons (to take into account intra-annual variations) and in other years (without restrictive and disinfection measures).

The work has financial support from RFBR, projects 19-05-00352 and 19-05-50088.