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Multiphase Mechanism for the Production of Sulfuric Acid from SO2 by Criegee Intermediates Formed During the Heterogeneous Reaction of Ozone with Squalene.


Here we report a new multiphase reaction mechanism by which Criegee intermediates (CIs), formed by ozone reactions at an alkene surface, convert SO2 to SO3 to produce sulfuric acid, a precursor for new particle formation (NPF). During the heterogeneous ozone reaction, in the presence of 220 ppb SO2, an unsaturated aerosol (squalene) undergoes rapid chemical erosion, which is accompanied by NPF. A kinetic model predicts that the mechanism for chemical erosion and NPF originate from a common elementary step (CI + SO2) that produces both gas phase SO3 and small ketones. At low relative humidity (RH = 5%), 20% of the aerosol mass is lost, with 17% of the ozone-surface reactions producing SO3. At RH = 60%, the aerosol shrinks by 30%, and the yield of SO3 is <5%. This multiphase formation mechanism of H2SO4 by CIs is discussed in the context of indoor air quality and atmospheric chemistry.

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