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.

This study presents airborne measurements of HO2NO2, HCl and SO2 using chemical ionization mass spectrometry (CIMS) during the Intercontinental Chemical Transport Experiment (INTEX) field campaign, an intensive study to characterize the chemical composition of the troposphere in the eastern United States, Mexico City, and the North Pacific which is the outflow region of Asia. The first direct in situ measurements of HO2NO2 were made in the free troposphere over the eastern U.S. during summer 2004. The highest mean mixing ratio of 76 pptv (median = 77 pptv, = 39 pptv) was observed in the altitude range of 8-9 km. Highly constrained steady state calculations of HO2NO2 using measured HOx levels are poorly correlated with observed HO2NO2 in the upper troposphere (8 km < z < 12 km; the median ratio of [HO2NO2]SS-MEA/[HO2NO2]MEA = 2.9). However, steady state HO2NO2 using model-derived HOx shows reasonable agreement with measurements in the free troposphere ([HO2NO2]SS-MEA/[HO2NO2]MEA = 1.3). The vertical distribution of HCl was measured over the north Pacific during May 2006 from the marine boundary layer (MBL) up to lower stratosphere. Recent stratospheric influence in the upper troposphere (8 km < z < 12 km) was efficiently identified from enhanced HCl (up to ~100 pptv) relative to very low background levels (< 2pptv). In the remote MBL, the acidification of seasalt aerosols by HNO3 appeared to be the major source of HCl, with level consistently over 20 pptv (up to 400 pptv). The distribution of SO2 was measured in the outflow region of the eastern U.S. and Asia; two major anthropogenic SO2 source regions. This study presents vertical and horizontal distributions of SO2 and relevant gas phase and aerosol parameters to characterize SO2 transport in the troposphere. SO2 in the boundary layer was efficiently transported to the upper troposphere by deep convection and frontal uplift processes. High SO2 in convective plume in the upper troposphere were strongly correlated with ultrafine aerosols.Conversely, SO2 from frontal uplift shows a strong correlation with non-volatile aerosols. Comparisons of SO2 products from global 3-D chemical transportation models (GEOS-CHEM and MOZART) with observations suggest that sulfur sources are relatively well described but that the oxidation mechanism needs refinement.