Thermal Inversions and Their Influence on the Composition of the Surface Air Layer over Moscow

Thermal stratification of the lower 800-m air layer over Moscow, including distribution functions of inversion heights and duration, has been studied in detail based on ECHO-1 sodar data. The distribution of the bottom height of elevated inversions, unlike the thickness of surface inversions, is bimodal, which reflects the diversity of their origin. The lifetime of morning elevated inversions (remains of night surface inversions) is, on average, ~ 3 h, and, in some cases, over 6 h; their bottom heights usually do not exceed 350 m. Superlong elevated subsidence inversions are more often observed in Moscow from November to February and may be detected on sodar records continuously up to 120 h. The influence of retentive inversion layers on the surface content of trace gases in the atmosphere over Moscow has been studied based on the 2002–2016 data. The final destruction of morning elevated inversions results in a rapid acceleration of increase in the content of O 3 and a start of decrease in the content of NO 2 in the atmospheric surface layer. Both effects reflect the intensification of a vertical turbulent exchange. Such a rapid increase in the rate of growth of ozone after the inversion destruction is not associated with its photochemical generation and is apparently the result of dynamic processes (increased downward ozone fluxes from upper air layers). In contrast, under the conditions of long-lived elevated subsidence inversions in fall and winter, no statistically significant variations in the surface contents of five trace gases (O 3 , NO, NO 2 , CO, and SO 2 ) have been found.