Ozone and its precursors dynamics in the megapolis atmospheric surface layer at radiation fog

A significant (many times) increase in the concentrations of ozone precursors (NO, NO 2 , CO, CH 4 and CH x ) in the surface atmospheric layer due to their accumulation under calm conditions was recorded during an episode of the radiation fog in Moscow early November 2021. At the same time the partial pressure of H 2 O vapor decreased by ∼30% due to water condensation during temperature drop. A strong correlation had been observed between the O 3 content and the ratio of nitrogen oxides’ concentrations NO 2 /NO at fog. In particular, the O 3 content dropped to zero values at fog. The latter can be attributed to the simultaneous action of several factors: the absence of photochemical ozone production at high NO concentrations, the absence of horizontal and vertical ozone transfer under calm, and the additional ozone runoff due to dissolution in fog microdroplets.