Abstract

The first measurements of peroxy (HO 2+ RO 2) and hydroxyl (OH) radicals above the arctic snowpack were collected during the summer 2003 campaign at Summit, Greenland. The median measured number densities for peroxy and hydroxyl radicals were 2.2×10 8 mol cm −3 and 6.4×10 6 mol cm −3, respectively. The observed peroxy radical values are in excellent agreement ( R 2 = 0.83 , M / O = 1.06 ) with highly constrained model predictions. However, calculated hydroxyl number densities are consistently more than a factor of 2 lower than the observed values. These results indicate that our current understanding of radical sources and sinks is in accord with our observations in this environment but that there may be a mechanism that is perturbing the (HO 2+ RO 2)/OH ratio. This observed ratio was also found to depend on meteorological conditions especially during periods of high winds accompanied by blowing snow. Backward transport model simulations indicate that these periods of high winds were characterized by rapid transport (1–2 days) of marine boundary layer air to Summit. These data suggest that the boundary layer photochemistry at Summit may be periodically impacted by halogens.

Highlights

  • Over the last decade the chemistry of the polar troposphere has received increased attentionS.J

  • The excellent agreement between modeled and observed values for HO2+RO2 indicates a good understanding of radical sources and sinks at Summit

  • The OH modeled to observed comparison is not as good, but improves substantially when filtered for high winds and averaged over the duration of the mission into a 24 h composite day

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Summary

Introduction

Over the last decade the chemistry of the polar troposphere has received increased attentionS.J. Over the last decade the chemistry of the polar troposphere has received increased attention. Atmospheric photochemistry in polar regions was expected to be rather inactive since the primary production of hydroxyl radicals (OH) is attenuated at high latitudes due to low dew points and large solar zenith angles. The presence of elevated NOx (NO+NO2) (Ridley et al, 2000; Honrath et al, 2002; Davis et al, 2001; Jones et al, 2000) can increase the oxidizing capacity of the polar troposphere by enhancing secondary production of OH through reactions (1) and (2).

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