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

The core information for this publication's citation.: 
Mao, J., D. Jacob, M. J. Evans, J. Olson, X. Ren, W. H. Brune, J. M. St. Clair, J. D. Crounse, K. M. Spencer, M. R. Beaver, P. Wennberg, M. J. Cubison, J. Jimenez-Palacios, A. Fried, P. Weibring, J. G. Walega, S. R. Hall, A. Weinheimer, R. C. Cohen, G. Chen, J. Crawford, C. S. McNaughton, A. Clarke, L. Jaeglé, J. A. Fisher, R. M. Yantosca, P. Le Sager, and C. Carouge (2010), Chemistry of hydrogen oxide radicals (HOx) in the Arctic troposphere in spring, Atmos. Chem. Phys., 10, 5823-5838, doi:10.5194/acp-10-5823-2010.
Abstract: 

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 (HOx ≡H+OH+peroxy radicals) and their reservoirs (HOy ≡HOx +peroxides) in the springtime Arctic atmosphere. We find that a standard gas-phase chemical mechanism overestimates the observed HO2 and H2 O2 concentrations. Computation of HOx and HOy gasphase chemical budgets on the basis of the aircraft observations also indicates a large missing sink for both. We hypothesize that this could reflect HO2 uptake by aerosols, favored by low temperatures and relatively high aerosol loadings, through a mechanism that does not produce H2 O2 . We implemented such an uptake of HO2 by aerosol in the model using a standard reactive uptake coefficient parameterization with γ (HO2 ) 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 HOx species and HOy reservoirs. HO2 uptake by aerosol is then a major HOx and HOy sink, decreasing mean OH and HO2 concentrations in the Arctic troposphere by 32% and 31% respectively. Better rate and product data for HO2 uptake by aerosol are needed to understand this role of aerosols in limiting the oxidizing power of the Arctic atmosphere.

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Research Program: 
Atmospheric Composition Modeling and Analysis Program (ACMAP)
Tropospheric Composition Program (TCP)
Mission: 
ARCTAS