Chemistry of hydrogen oxide radicals (HOₓ) in the Arctic troposphere in spring
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Date
2010-07-01
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Mao, J., Jacob, D. J., Evans, M. J., Olson, J. R., Ren, X., Brune, W. H., Clair, J. M. St., 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, P., and Carouge, C.: Chemistry of hydrogen oxide radicals (HOx) in the Arctic troposphere in spring, Atmos. Chem. Phys., 10, 5823–5838, https://doi.org/10.5194/acp-10-5823-2010, 2010.
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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 H₂O₂ concentrations. Computation of HOₓ and HOy 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 HO₂ 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 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.