Measurements of OH Reactivity Using a Chemical Ionization Mass Spectrometry Technique

Typically tropospheric chemical models overestimate [OH] when compared to measurements. This discrepancy is usually attributed to incompletely modeling OH sinks due to a lack of measurements. The determination of OH reactivity provides an independent means to quantify the overall contribution of these unmeasured trace species to OH oxidation. Therefore, a new instrument was developed to measure the total loss rate of OH to chemical species in ambient air using the CIMS technique. Measurements were performed as part of two field campaigns, the Nucleation in Forests (NIFTy) study in Indiana during May 2008 and the Ocean-Atmosphere-Sea Ice- Snowpack (OASIS) Spring 2009 intensive near Barrow, Alaska. The NIFTy study provided an opportunity to intercompare with a second OH reactivity system using the laser induced fluorescence detection technique as well as measure in an environment that has published results to compare to. The OASIS study provided an opportunity to measure in a previously unmeasured environment with a suite of complimentary measurements to allow for comparison between measured and calculated OH reactivity. The results of the NIFTy study showed good agreement between the two instruments as well as previous published results for forest and mixed use environments. OASIS provided the first ground based measurements of OH reactivity in the Arctic and the lowest average for measured OH reactivity of published results, about 2.5 s-1. OH reactivity was found to be lower during ozone depletion events than non-ozone depletion events, but not significantly