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

• Main Authors: Mao, J, Jacob, D J, Evans, M J, Olson, J R, Ren, X, Brune, W H, St. Clair, T 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, Jaegle, L, Fisher, Jenny A, Yantosca, R M, Le Sager, P, Carouge, C C
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Research Online 2010
• Subjects: troposphere; arctic; spring; hox; chemistry; radicals; oxide; hydrogen; Life Sciences; Physical Sciences and Mathematics; Social and Behavioral Sciences; Arctic
• Online Access: https://ro.uow.edu.au/scipapers/4692; https://ro.uow.edu.au/cgi/viewcontent.cgi?article=8035&context=scipapers

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.