Mao, JialinJacob, DanielEvans, M. J.Olson, J. R.Ren, X.Brune, W. H.St. Clair, J. M.Crounse, J. D.Spencer, K. M.Beaver, M. R.Wennberg, P. O.Cubison, M. J.Jimenez, J. L.Fried, A.Weibring, P.Walega, J. G.Hall, S. R.Weinheimer, A. J.Cohen, R. C.Chen, G.Crawford, J. H.McNaughton, C.Clarke, A. D.Jaeglé, L.Fisher, J. A.Yantosca, R. M.Le Sager, PCarouge, C.2014-03-172010Mao, Jialin, Daniel J. Jacob, M. J. Evans, J. R. Olson, X. Ren, W. H. Brune, J. M. St. Clair, et al. 2010. “Chemistry of Hydrogen Oxide Radicals \((HO_x)\) in the Arctic Troposphere in Spring.” Atmospheric Chemistry and Physics 10 (13) (July 1): 5823–5838. doi:10.5194/acp-10-5823-2010. http://dx.doi.org/10.5194/acp-10-5823-2010.1680-73161680-7324http://nrs.harvard.edu/urn-3:HUL.InstRepos:11913975We 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 \(H_2O_2\) 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 H2O2. We implemented such an uptake of \(HO_2\) by aerosol in the model using a standard reactive uptake coefficient parameterization with \(\gamma(HO_2)\) 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.en-USJournal Article2014-03-1710.5194/acp-10-5823-2010