The effect of nitric acid uptake on the deliquescence and efflorescence of binary ammoniated salts in the upper troposphere

Abstract

Thermodynamic equilibrium model calculations are used to show that HNO3 can lower the relative humidity barrier to deliquesce binary ammoniated salts in the upper troposphere, particularly in aerosol solutions with an (NH4)2SO4 composition. Also in the case of (NH4)2SO4 or NH4HSO4 there is no abrupt change in the physical state of the thermodynamic system (instantaneous change of a dry salt particle into an aqueous solution) at the deliquescent point, which is typical for such a phase transition. Model results show that HNO3 dissolution in ammoniated aerosol solutions can prevent the efflorescence of (NH4)2SO4 and NH4HSO4 salts in favor of (NH4)3H(SO4)2 (letovicite) crystallization. Future laboratory experiments, where binary ammoniated salts are studied at cold temperatures in the presence of both HNO3 and H2O, are needed to confirm the results of our model calculations.