An assessment of the polar HOx photochemical budget based on 2003 Summit Greenland field observations

Authors

Gao Chen, NASAFollow
L Gregory Huey, Georgia Institute of Technology - Main Campus
J H. Crawford, Georgia Institute of TechnologyFollow
J R. Olson, NASA
Manuel Hutterli, University of Arizona
D Tanner, Georgia Institute of Technology - Main Campus
Jack E. Dibb, University of New HampshireFollow
Barry Lefer, University of Houston - Main
N J. Blake, University of California, IrvineFollow
D D. Davis, Georgia Institute of Technology
Andreas Stohl, Norwegian Institute for Air Research
S. Sjostedt, Georgia Institute of Technology - Main Campus

Abstract

An interpretative modeling analysis is conducted to simulate the diurnal variations in OH and HO₂+RO₂ observed at Summit, Greenland in 2003. The main goal is to assess the HO_x budget and to quantify the impact of snow emissions on ambient HO_x as well as on CH₂O and H₂O₂. This analysis is based on composite diurnal profiles of HO_x precursors recorded during a 3-day period (July 7–9), which were generally compatible with values reported in earlier studies. The model simulations can reproduce the observed diurnal variation in HO₂+RO₂ when they are constrained by observations of H₂O₂ and CH₂O. By contrast, model predictions of OH were about factor of 2 higher than the observed values. Modeling analysis of H₂O₂ suggests that its distinct diurnal variation is likely controlled by snow emissions and loss by deposition and/or scavenging. Similarly, deposition and/or scavenging sinks are needed to reproduce the observed diel profile in CH₂O. This study suggests that for the Summit 2003 period snow emissions contribute ∼25% of the total CH₂O production, while photochemical oxidation of hydrocarbon appears to be the dominant source. A budget assessment of HO_x radicals shows that primary production from O(¹D)+H₂O and photolysis of snow emitted precursors (i.e., H₂O₂ and CH₂O) are the largest primary HO_x sources at Summit, contributing 41% and 40%, respectively. The snow contribution to the HO_x budget is mostly in the form of emissions of H₂O₂. The dominant HO_x sink involves the HO₂+HO₂ reaction forming H₂O₂, followed by its deposition to snow. These results differ from those previously reported for the South Pole (SP), in that primary production of HO_x was shown to be largely driven by both the photolysis of CH₂O and H₂O₂ emissions (46%) with smaller contributions coming from the oxidation of CH₄ and the O(¹D)+H₂O reaction (i.e., 27% each). In sharp contrast to the findings at Summit in 2003, due to the much higher levels of NO_x, the SP HO_x sinks are dominated by HO_x–NO_x reactions, leading to the formation and deposition of HNO₃and HO₂NO₂. Thus, a comparison between SP and Summit studies suggests that snow emissions appear to play a prominent role in controlling primary HO_x production in both environments. However, as regards to maintaining highly elevated levels of OH, the two environments differ substantially. At Summit the elevated rate for primary production of HO_x is most important; whereas, at SP it is the rapid recycling of the more prevalent HO₂radical, through reaction with NO, back to OH that is primarily responsible.

Department

Earth Sciences, Earth Systems Research Center

Publication Date

11-2007

Journal Title

Atmospheric Environment

Publisher

Elsevier

Digital Object Identifier (DOI)

10.1016/j.atmosenv.2007.06.014

Document Type

Article

Recommended Citation

G. Chen, L.G. Huey, J.H. Crawford, J.R. Olson, M.A. Hutterli, S. Sjostedt, D. Tanner, J. Dibb, B. Lefer, N. Blake, Douglas Davis, A. Stohl, An assessment of the polar HOx photochemical budget based on 2003 Summit Greenland field observations, Atmospheric Environment, Volume 41, Issue 36, November 2007, Pages 7806-7820, ISSN 1352-2310, http://dx.doi.org/10.1016/j.atmosenv.2007.06.014.

Rights

Copyright © 2007 Elsevier Ltd. All rights reserved.