Sulfate or Organic Acids: The Atmospheric Fate of Stabilized Criegee Intermediates

Stabilized Criegee intermediates (SCIs) are one of the key products formed during the gas-phase ozonolysis of unsaturated volatile organic compounds (VOCs), which are abundant in urban and industrial emissions as well as biogenic emissions from forested areas. We performed theoretical analyses and regional model simulations to evaluate how different sets of reaction rate coefficients affect the formation of sulfate and organic acids from SCI reactions. Our results reveal that both summer and winter conditions result in high organic acid yields and low sulfate yields, leading to increases in hourly formic acid and higher organic acids by as much as 1–3 ppb regardless of the set of reaction rate coefficient used, which can contribute to significant increases in water-soluble secondary organic aerosol under typical ambient conditions in forested areas in China and Southeast Asia. Comparison of modeled SCI concentrations with estimated ambient SCI concentrations in forested areas in northern Europe provides the first regional modeling evidence that larger SCIs may react more slowly with H₂O than small SCIs such as HCHO₂, implying that reactions of larger SCIs with SO₂ may also lead to increased sulfate concentrations, especially in highly polluted areas.