Hydrogen oxide photochemistry in the northern Canadian spring time boundary layer

Abstract

Measurements of OH and HO 2 concentrations were made at the surface of the eastern coast of the Hudson Bay during the COBRA campaign from February 18th to March 8th 2008. Diurnally averaged OH and HO 2 concentrations peaked at 1.16 (±1.02) × 10 6 molecule cm -3 and 1.42 (±0.64) × 10 8 molecule cm -3 respectively. A box-model, constrained to supporting observations, is used to access the radical budget in this cold, northerly environment. Formaldehyde (HCHO) photolysis is found to be the dominant daytime radical source, providing 74% of the observed HO x. A considerable (>80% of the total source) surface HCHO source is required to reconcile the model and observed HCHO concentrations. Model simulations also suggest significant roles for the heterogeneous loss of HO 2 and for halogen chemistry in the cycling of HO 2 to OH. The formation of HO 2 NO 2 is identified as an important radical reservoir, reducing HO x concentrations during the day and enhancing them at night. This impacts both local oxidizing capacity and reduces local ozone production by approximately 30%. The sensitivity of the local chemistry to uncertainties in these processes is explored. The majority of these processes are not currently represented in global chemistry models. Copyright 2011 by the American Geophysical Union.