Accretion Product Formation from Self- and Cross-Reactions of RO2 Radicals in the Atmosphere

Abstract

Hydrocarbons are emitted into the Earth's atmosphere in very large quantities by human and biogenic activities. Their atmospheric oxidation processes almost exclusively yield RO₂ radicals as reactive intermediates whose atmospheric fate is not yet fully unraveled. Herein, we show that gas-phase reactions of two RO₂ radicals produce accretion products composed of the carbon backbone of both reactants. The rates for accretion product formation are very high for RO₂ radicals bearing functional groups, competing with those of the corresponding reactions with NO and HO₂ . This pathway, which has not yet been considered in the modelling of atmospheric processes, can be important, or even dominant, for the fate of RO₂ radicals in all areas of the atmosphere. Moreover, the vapor pressure of the formed accretion products can be remarkably low, characterizing them as an effective source for the secondary organic aerosol.

Keywords: accretion products; atmospheric chemistry; mass spectrometry; radical reactions.