Heterogeneous reactions with NaCl in the El Chichon volcanic aerosols

Abstract

Previous investigations of the effects of the 1982 eruption of the El Chichon volcano could not explain all the observations of changes in O3, HCl, NO and NO2 simultaneously without proposing unproven chemical reactions. Since reactions between solid NaCl and gaseous ClNO3 and N2O5 rapidly produce photochemically active chlorine species and solid NaNO3 in laboratory experiments, we suggest that these reactions could have occurred with the NaCl observed to be present in the El Chichon sulfuric acid aerosols. As a consequence, we predict that HCl should increase substantially, while NOx should decrease, in agreement with the measurements after the eruption. Ozone should only be slightly affected by these reactions. Reactions between solid NaCl and the acids H2SO4 and HNO3 might prove to be important, but we lack sufficient evidence regarding their efficiency and the presence of HNO3 in the aerosols to be more conclusive.