Sub-urban OH response to isoprene chemistry: A case study in the Dallas-Ft Worth Area

Recently, multiple studies have reported discrepancies in measured and model-predicted OH concentrations in high isoprene areas. Isoprene oxidation chemistry initiated by OH, for this reason, has been reevaluated in the past few years. The research results, mostly from laboratory and theoretical studies postulated a number of new radical chemistry mechanisms that can potentially explain the discrepancy between observed and model predicted OH. However, these proposed chemical mechanisms have not been fully tested by field measurement data. During the DFW-2011 field campaign at a suburban air-pollution observatory in the Dallas-Ft. Worth area, OH and reactive gases (CO, NOx, ozone, and VOCs) were observed in the month of June, 2011. Over the month, we observed a wide range of isoprene concentrations. Therefore, the dataset provides opportunities to evaluate the newly proposed mechanisms under ambient conditions. Especially, we will present a VOC dataset measured by the PTR-ToF-MS instrumentation, which provides extensive information on conventionally unmeasured isoprene oxidation products. These compounds such as C4 and C5 hydroxycarbonyl compounds have not been measured routinely in ambient conditions due to technical difficulties but are needed to assess the newly proposed isoprene oxidation mechanisms. During the presentation, we will closely examine how isoprene oxidation will affect ambient OH distributions in the suburban environment followed by interpretation of how the OH levels affect local ozone and aerosol formation processes