Calculated Absorption Cross Sections and Photolysis Rates of Hydroperoxyaldehydes

Hydroperoxyaldehydes are a class of compounds frequently formed in the atmosphere from oxidation of emitted volatile organic compounds. One recently detected example is hydroperoxymethyl thioformate (HPMTF), which is formed in large quantities from the widely emitted dimethyl sulfide. Understanding the atmospheric fate of HPMTF, including the contribution of photolysis, is crucial for quantifying its impacts on important atmospheric outcomes such as sulfate production. We have used a nuclear ensemble approach to calculate the electronic absorption cross section of three test molecules, HPMTF, and selected hydroperoxyaldehydes. We use the calculated absorption spectra to estimate the atmospheric photolysis rates of the hydroperoxyaldehydes. We implement the calculated absorption cross section of HPMTF into a global atmospheric model and find that photolysis is only a minor loss path for HPMTF. We show that photolysis rates obtained using structure-activity relationship approaches based on the functional groups of molecules are unreliable, because these approaches ignore effects from heteroatoms. For hydroperoxyaldehydes with oxygen or nitrogen in the α-position to the carbonyl group, we find that photolysis is insignificant, due to strong heteroatom effects.