Moscow megacity has a big gap in assessment of air quality, resulting in severe aerosol pollution. Black carbon (BC) concentrations over different timescales, including weekly and diurnal, are studied during four seasons of 2019–2020 at urban background site. Seasonal BC varies from 0.9 to 25.5 μg/m3 with a mean of 1.7 ± 1.4 μg/m3. Maximum mean BC equal to 2.2 ± 1.8 μg/m3 was observed in spring. Diurnal trends of black carbon concentrations differ in spring/summer and autumn/winter periods, they exhibit morning and evening peaks corresponding to traffic combined with the boundary layer height effect. The weekly cycle of BC characterizes the highest amount of combustion-related pollution on working days and the characteristics of population migration from a city for weekend. Seasonal pollution roses show the direction of the highest BC contamination. For identification of BC sources relating to traffic, heat and power plants, and industry around the site, polar plots are used. The spectral dependence of the aerosol light attenuation provides the estimate for Absorption Angstrom Exponent (AAE). We use the AAE above 1.3 and high frequency of AAE observation above 1 in order to support the assessment for a contribution of biomass burning in the region around Moscow in autumn and winter as well as of agriculture fires and wildfires in warm seasons. Air masses arriving to a city from fire-affected regions in spring and summer impact urban air pollution.

The COVID-19 pandemic has led to self-isolation and business interruptions around the world. On the basis of measurements of concentrations of an indicator of aerosol emissions from fuel combustion products-black carbon-it is shown that the decrease in economic activity had a significant effect on the pollution of the Moscow atmosphere. The decrease in the intensity of the traffic and the change in the operating mode of industrial and heat-and-power enterprises of the city during the period of restrictive measures in the spring of 2020 were determined by the dynamics of the daily and weekly trend of black carbon levels. The decrease in the fraction of fossil fuel combustion at this time correlates with the increased contribution of biomass combustion in the residential sector and during agricultural fires around the megalopolis. Changes in the intensity and direction of sources of high concentrations of black carbon were observed during the recovery of economic activity in the summer of 2020. The decrease in the concentration of black carbon and fine particles less than 2.5 μm in size (PM2.5) in the urban atmosphere reflects a decline in economic activity and an improvement in air quality and conditions for maintaining the health of the Moscow population during the COVID-19 pandemic.

The impact of aerosol sources on the pollution of the Russian sector of the Arctic is now strongly underestimated. A new polar aerosol station was arranged in August 2019 on Bely Island (Kara Sea), on the pathway of air mass transport from industrial regions of Western Siberia to the Arctic. Continuous aethalometer measurements of a short-lived climate tracer, i.e., black carbon, (from December to April 2019 and from January to November 2020) showed its seasonal variations with high values (60–92 ng/m3) in December–April and low values (18–72 ng/m3) in June–September. Pollution periods are identified. Regional distribution of fossil fuel and biomass combustion sources are obtained using the black carbon concentration weight trajectory model. The impact of gas flaring from oil and gas extraction areas of Western Siberia, the Volga region, the Urals, and the Komi Republic is found to be most pronounced during the cold period, and the impact from wildfire smoke emissions is found to be maximal in the warm season. A marker of biomass burning impact, determined from the difference between the black carbon concentrations measured in a broad wavelength spectrum, indicated the predominant effects from residential wood combustion in the cold period and agricultural and forest fires in the warm season.