Chemistry of hydrogen oxide radicals (HO x ) in the Arctic troposphere in spring

• Published in: Atmospheric Chemistry and Physics
• Main Authors: L. Jaeglé, C. McNaughton, A. D. Clarke, J. H. Crawford, G. Chen, R. C. Cohen, A. J. Weinheimer, S. R. Hall, J. G. Walega, P. Weibring, A. Fried, J. L. Jimenez, M. J. Cubison, P. O. Wennberg, M. R. Beaver, K. M. Spencer, J. D. Crounse, J. M. St. Clair, W. H. Brune, X. Ren, J. R. Olson, M. J. Evans, D. J. Jacob, J. Mao, J. A. Fisher, R. M. Yantosca, P. Le Sager, C. Carouge
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2010
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Arctic
• Online Access: https://doi.org/10.5194/acp-10-5823-2010; https://doaj.org/article/b33d5c1240ae4451bf203debc1fd27b9

We use observations from the April 2008 NASA ARCTAS aircraft campaign to the North American Arctic, interpreted with a global 3-D chemical transport model (GEOS-Chem), to better understand the sources and cycling of hydrogen oxide radicals (HO x ≡H+OH+peroxy radicals) and their reservoirs (HO y ≡HO x +peroxides) in the springtime Arctic atmosphere. We find that a standard gas-phase chemical mechanism overestimates the observed HO 2 and H 2 O 2 concentrations. Computation of HO x and HO y gas-phase chemical budgets on the basis of the aircraft observations also indicates a large missing sink for both. We hypothesize that this could reflect HO 2 uptake by aerosols, favored by low temperatures and relatively high aerosol loadings, through a mechanism that does not produce H 2 O 2 . We implemented such an uptake of HO 2 by aerosol in the model using a standard reactive uptake coefficient parameterization with γ(HO 2 ) values ranging from 0.02 at 275 K to 0.5 at 220 K. This successfully reproduces the concentrations and vertical distributions of the different HO x species and HO y reservoirs. HO 2 uptake by aerosol is then a major HO x and HO y sink, decreasing mean OH and HO 2 concentrations in the Arctic troposphere by 32% and 31% respectively. Better rate and product data for HO 2 uptake by aerosol are needed to understand this role of aerosols in limiting the oxidizing power of the Arctic atmosphere.