Investigation of Photochemistry at High Latitudes: Comparison of model predictions to measurements of short lived species
Sjostedt, Steven Jeffrey
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Recent field campaigns have measured enhanced levels of NOx (NO+NO2) and HOx precursors (i.e., H2O2, CH2O, and HONO) that can not be accounted for by gas phase chemistry alone. Snowpack emission is now considered a source of these species. Therefore, the photochemistry in the polar boundary layer is now believed to be much more complex than initially thought. Field campaigns to Summit, Greenland in the summer of 2003 and the spring of 2004 have obtained the first measurements of peroxy (HO2+RO2) and hydroxyl (OH) radicals in the Artic boundary layer. Measurements were collected with a chemical ionization mass spectrometer (CIMS). A highly constrained (ie., O3, H2O, CH4, CO, j-values, NO, H2O2,CH2O, and HONO) 0-D steady-state model was employed in order to test our current understanding of photochemistry. HO2+RO2 measurements were in excellent agreement with model predictions for both spring and summer. OH measurements were in good agreement with spring model predictions but were a factor of two greater than summer model predictions. The role of snowpack emission is also addressed in a HOx budget performed on the spring campaign. Measurements of nitric acid (HNO3) and pernitric acid (HO2NO2) were obtained with the CIMS during the Antarctic Tropospheric Chemistry Investigation (ANTCI). The linkage between HOx and NOx chemistry is examined through partitioning of reactive nitrogen between HNO3 and HO2NO2. The possible impact of reactive nitrogen partitioning on nitrate ions (NO3-) at coring sites is also investigated.