PAUL BRADFORD SHEPSON

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Forest emissions of biogenic volatile organic compounds (BVOCs), such as isoprene and other terpenes, play a role in the production of tropospheric ozone and aerosols. In a northern Michigan forest, the direct measurement of total OH reactivity, which is the inverse of the OH lifetime, was significantly greater than expected. The difference between measured(More)
Bromine atoms are believed to play a central role in the depletion of surface-level ozone in the Arctic at polar sunrise. Br2, BrCl, and HOBr have been hypothesized as bromine atom precursors, and there is evidence for chlorine atom precursors as well, but these species have not been measured directly. We report here measurements of Br2, BrCl, and Cl2 made(More)
Following the springtime polar sunrise, ozone concentrations in the lower troposphere episodically decline to near-zero levels 1. These ozone depletion events are initiated by an increase in reactive bromine levels in the atmosphere 2–5. Under these conditions, the oxidative capacity of the Arctic troposphere is altered, leading to the removal of numerous(More)
Photolysis of nitrous acid generates hydroxyl radicals—a key atmospheric oxidant—in the lower atmosphere. Significant concentrations of nitrous acid have been reported in the rural atmospheric boundary layer during the day, where photolysis of nitrous acid accounts for up to 42% of sunlight-induced radical production 1–7. The observed concentrations of(More)
Isoprene hydroxynitrates (IN) are tracers of the photochemical oxidation of isoprene in high NO x environments. Production and loss of IN have a significant influence on the NO x cycle and tropospheric O 3 chemistry. To better understand IN chemistry, a series of photochemical reaction chamber experiments was conducted to determine the IN yield from(More)
Multiple axis differential absorption spectroscopy (MAX-DOAS) measurements of bromine monoxide (BrO) probed the vertical structure of halogen activation events during March–May 2012 at Barrow, Alaska. An analysis of the BrO averaging kernels and degrees of freedom obtained by optimal-estimation-based inversions from raw MAX-DOAS measurements reveals the(More)
This discussion paper is/has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP if available. Abstract The springtime depletion of tropospheric ozone in the Arctic is known to be caused by active halogen photochemistry resulting from halogen atom precursors emitted from snow, ice,(More)