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The location of Moscow on a plain within higher latitudes when compared to other megacities creates conditions for the chemical transformation of pollutants in the urban atmosphere and their transport and accumulation. Observational data on surface concentrations of NO, NO2, CO, CH4, O3, nonmethane hydrocarbons (NMHCs), and aerosols (PM10), which were obtained at the Moscow Ecological Monitoring (MEM) network from 2005 to 2020, have been processed and analyzed. Both temporal and spatial parameters characterizing the dynamics of atmospheric pollution of Moscow's air basin have been calculated. It is noted that the content of most pollutants in the urban air has decreased due to the renewal of the vehicle fleet; the introduction of restrictions on the entry of freight transport in the city; and the modernization of industrial enterprises, treatment facilities, and the gas transmission system. Significant negative trends have been obtained for NMHCs, CO, NOx, and PM10 (4.3, 4.0, 2.6, and 1.7% y–1, respectively). An insignificant negative trend has been obtained for O3 and no negative trend has been found for CH4. Total emissions from urban sources of substances determining the air quality have been calculated. Their values also manifest negative trends. The content of ozone almost did not change within such a long period, which suggests a weak sensitivity of the oxidizing properties of the Moscow atmosphere and the rate of ozone generation to variations in the atmospheric content of nitrogen radicals and their high sensitivity to volatile organic compounds. [ABSTRACT FROM AUTHOR]