Abstract
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.
Highlights
Radiative forcing by aerosol and tropospheric ozone pollution transported from mid-latitudes may be an important driver of recent Arctic warming (Quinn et al, 2008; Shindell et al, 2008)
The Tropospheric Ozone Production about the Spring Equinox (TOPSE) aircraft campaign conducted a series of flights in the North American Arctic from February to May of 2000 including measurements of total peroxy radicals (Cantrell et al, 2003a), HCHO (Fried et al, 2003), and peroxides (Snow et al, 2003) up to 8 km altitude
GEOS-Chem is a global 3-D chemical transport model driven by assimilated meteorological observations from the Goddard Earth Observing System (GEOS-5) of the NASA Global Modeling and Assimilation Office (GMAO) (Bey et al, 2001)
Summary
Radiative forcing by aerosol and tropospheric ozone pollution transported from mid-latitudes may be an important driver of recent Arctic warming (Quinn et al, 2008; Shindell et al, 2008). Past studies of HOx chemistry in Arctic spring have mainly been from surface sites They have pointed out the importance of HOx radical production from photochemically driven snow emissions of H2O2 (Hutterli et al, 2001; Jacobi et al, 2002), HCHO (Sumner and Shepson, 1999; Sumner et al, 2002), and HONO (Zhou et al, 2001). The Tropospheric Ozone Production about the Spring Equinox (TOPSE) aircraft campaign conducted a series of flights in the North American Arctic from February to May of 2000 including measurements of total peroxy radicals (Cantrell et al, 2003a), HCHO (Fried et al, 2003), and peroxides (Snow et al, 2003) up to 8 km altitude. This ensemble of observations offers strong constraints and a new perspective on the factors controlling HOx concentrations in the Arctic spring troposphere
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