HO_<i>x</i> budgets in a deciduous forest: Results from the PROPHET summer 1998 campaign

Abstract

Results from a tightly constrained photochemical point model for OH and HO 2 are compared to OH and HO 2 data collected during the Program for Research on Oxidants: Photochemistry, Emissions, and Transport (PROPHET) summer 1998 intensive campaign held in northern Michigan. The PROPHET campaign was located in a deciduous forest marked by relatively low NO x levels and high isoprene emissions. Detailed HO x budgets are presented. The model is generally unable to match the measured OH, with the observations 2.7 times greater than the model on average. The model HO 2 , however, is in good agreement with the measured HO 2 . Even with an additional postulated OH source from the ozonolysis of unmeasured terpenes, the measured OH is 1.5 times greater than the model; the model HO 2 with this added source is 15% to 30% higher than the measured HO 2 . Moreover, the HO 2 /OH ratios as modeled are 2.5 to 4 times higher than the measured ratios, indicating that the cycling between OH and HO 2 is poorly described by the model. We discuss possible reasons for the discrepancies.