Constraining the Acetone Photolysis Quantum Yield: Current Insights and Atmospheric Chemistry Implications

Abstract

Acetone photolysis is a potentially important source of hydroperoxyl and hydroxyl radicals (HO_x) to the upper troposphere. The extent to which acetone photolysis is a significant source of HO_x in the upper troposphere is unclear in part because of scarce measurements of the acetone photolysis quantum yield (Φ_acetone) in the actinic region (i.e., λ > 300 nm). Past measurements of the Φ_acetone have derived temperature- and pressure-dependent parameterizations that lead to significantly different conclusions about the importance of acetone to HO_x formation in the upper troposphere. Here, we focus on previously published data to derive the recommended Φ_acetone for atmospheric chemical modeling. Using Stern-Volmer analyses, we determine temperature- and pressure-dependent Φ_acetone using updated measurements of fundamental acetone photolysis parameters. We also use simulations of the Φ_acetone produced from recent photophysical modeling to derive temperature- and pressure-dependent parameterizations of the Φ_acetone. In contrast to the current Φ_acetone parameterization used in atmospheric chemical modeling, our parameterization reflects a predicted nonzero Φ_acetone in the wavelength region above 320 nm. Despite the increased Φ_acetone values in the higher wavelength region of the acetone photolysis action spectrum, the modeled effect on HO_x production is not significantly different from HO_x produced using the current recommended Φ_acetone parameterization. Uncertainties in the acetone photolysis mechanism remain; thus, more direct temperature- and pressure-dependent measurements of Φ_acetone are warranted.