Role of coarse and fine nitrate particulate as source of snow nitrate in the High Arctic

Arctic aerosols have been extensively measured in several sites, such as Alaska, Greenland and European Arctic (Beine et al., 2003). However the actual understanding on their sources and influence on the Arctic chemistry and climate has remained far from complete. Atmospheric inorganic nitrate (NO3-) occurs as gaseous nitric acid (HNO3) and particulate nitrate (p-NO3-) in the coarse and fine fractions. The major chemical processes, producing atmospheric NO3-, are indicated in Table 1. Both HNO3 and p-NO3- are thermodynamically stable and highly soluble and their ultimate sinks are wet and dry depositions affecting the snow NO3- budget. The fate of snow NO3- depends on post-depositional processes, such the evaporation of gaseous HNO3 and the photolysis of snow NO3-. The latter produces gaseous reactive nitrogen species (NO, NO2 and nitrous acid, HONO) in the in snow, which can be released to the overlaying atmosphere, affecting the overall budget of HOx radicals, NOx, and ozone (O3). The chemical and physical properties of the atmosphere (solar radiation, temperature, and the concentration of pollutants) and snow (temperature, hardness, density, reflectance, specific surface area, size and shape of snow grains, penetration of UV radiation, snow accumulation rate, pH, and ionic strength) can affect the magnitude of these post-depositional processes. Previous studies showed that snow NO3- concentration changes seasonally with a summer maximum and a winter minimum, due to the active photochemical reactions during polar summer when other NOx reservoir species (such as peroxyacetyl nitrate, PAN) and snowpack NO3- act as local NOx sources by recycling reaction (Geng et al. 2014). Measurements performed during the "Alert 2000" campaign highlighted that the dominant source for snow NO3- was wet deposition during snowfall (Ianniello et al., 2002). Recently, the microbial activity within the snow has been proposed to produce nitrogen monoxide (NO), HONO and HNO3 (Amoroso et al., 2010). In addition, detailed sampling of surface snow during winter and springtime at Ny-Ålesund demonstrated that NO3- dry deposition is the predominant process determining NO3- concentrations during precipitation-free periods and prevails over any NO3- postdeposition losses via photolysis and HNO3 evaporation within (Björkman et al., 2014). In conclusion, although atmospheric inorganic NO3- seems likely to be an important source of snow NO3-, its real contribution is still uncertain. and there are still cognitive gaps related to the sources of snow NO3-. Here we reports the results from a field experiment performed at Ny-Ålesund (Svalbard) during spring of 2010 in order to investigate the sources and sinks of snow NO3-. References: Amoroso, A., Dominè, F., Esposito, G., Morin, S., Savarino, J., Nardino, M., Montagnoli, M., Bonneville, M., Clement, J.-C., Ianniello, A. and Beine, H.J. (2010) Environ. Sci. Technol. 44, 714-719. Beine, H.J., Dominè, F., Ianniello, A., Nardino, M., Allegrini, I., Teinilä, K. and Hillamo, R. (2003) Atmos. Chem. Phys. 3, 335-346. Bjorkman, M.P., Vega, C.P., Kuhnel, R., Spataro, F., Ianniello, A., Esposito, G., Kaiser, J., Marca, A., Hodson, A., Isaksson, E., and Roberts, T.J. (2014) J. Geophys. Res. Atmos. 119, 12,953-12,976. Geng, L., Cole-Dai, J., Alexander, B., Erbland, J., Savarino, J., Schauer, A.J., Steig, E.J., Lin, P., Fu, Q. and Zatko, M.C. (2014) Atmos. Chem. Phys. 14, 13361-13376. Ianniello, A., Beine, H.J., Sparapani, R., Di Bari, F., Allegrini, I. and Fuentes, J. (2002) Atmos. Environ. 36, 5299-5309.