Heterogeneous interactions of calcite aerosol with sulfur dioxide and sulfur dioxide–nitric acid mixtures

Abstract

The heterogeneous chemistry of sulfur dioxide with CaCO₃ (calcite) aerosol as a function of relative humidity (RH) has been studied under isolated particle conditions in an atmospheric reaction chamber using infrared absorption spectroscopy. The reaction of SO₂ with calcite produced gas phase CO₂ as a product in addition to the conversion of the particulate carbonate to sulfite. The reaction extent was found to increase with elevated RH, as has been observed for the similar reaction with HNO₃, but much higher relative humidities were needed to significantly enhance the reaction. Mixed experiments in which calcite aerosol was exposed to both HNO₃ and SO₂ were also performed. The overall reaction extent at a given relative humidity did not appear to be increased by having both reactant gases present. The role of carbonate aerosol as an atmospheric sink for sulfur dioxide and particulate nitrogen and sulfur correlations are discussed.