Observations of Non-OH Oxidants of SO2 during NOMADSS and FRAPPE

Abstract:

Oxidation is a key atmospheric process and impacts such issues as climate change, air quality, and acid rain. Current belief is that reactions involving OH and NO₃ to be the predominate mechanism in initiating removal processes. Towards understanding these oxidative processes, the CIMS techniques for measuring OH radicals was developed. As part of this measurement a determination of non-OH SO­­­₂ oxidants is made. This measurement has already changed the outlook of oxidation supporting the recent discovery that stabilized Criegee radicals (sCI) also have a significant capacity to oxidize compounds such as SO₂ to ultimately form H₂SO₄. Here we present measurements of non-OH SO₂ oxidants obtained during the Front Range Air Pollution and Photochemistry Experiment (FRAPPE) and the Nitrogen, Oxidants, Mercury, and Aerosol Distribution Sources and Sinks (NOMADSS) field campaigns. Both of these campaigns provided the opportunity to sample a broad spectrum of atmospheric environments ranging from biogenic to urban influenced air masses. These measurements reveal the sources to derive from surface emissions, with the largest concentrations observed in the boundary layer. Large non-OH SO₂ oxidant concentrations are seen over areas with large emissions of biogenic species such as isoprene, supporting the idea that they are mainly stabilized Criegee radicals. However large concentrations are also seen in areas of urban outflow, possibly indicating that there may be non-OH species other than stabilized Criegees which can oxidize SO₂.