Multiphase chemistry of NO₃ in the remote troposphere

The effect of NO 3 uptake at night into marine aerosol and cloud droplets on (1) sulfur oxidation, (2) NO 3 ambient concentrations, and (3) NO 3 atmospheric lifetime is examined using a simple chemical kinetics model. It is shown that the atmospheric lifetime toward multiphase removal of NO 3 is < 10 min in presence of cloud droplets. We also show that at low mixing ratios of H 2 O 2 (<150 pmol/mol), NO 3 can enhance sulfur oxidation in clouds via a catalytic cycle with a chain length of ∼8. Finally, in presence of sea‐salt aerosol, the uptake of NO 3 leads to low ambient concentrations of NO 3 , efficient S(IV) oxidation, and possibly, to release of halogens from the aerosol. The results of this study imply that the multiphase reaction of NO 3 may be important in the remote marine boundary layer.