Fractionation of inorganic nitrates in winter Arctic troposphere: Coarse aerosol particles containing inorganic nitrates

Atmospheric aerosol particles and acidic gases were collected at Ny-Alesund, Norwegian high Arctic, in winter (December - March) of 1994/1995, 1995/1996 and 1996/1997 to understand the sink processes of atmospheric inorganic nitrate and reactive nitrogen or;ides. Atmospheric inorganic nitrates were mostly present as particulate NO3- in the coarse mode defined as diameter >2.3 mu m) of which major constituents were sea-salt compounds such as Nai and Cl-. The number fraction of coarse aerosol particles containing NO3- increased in aged oceanic air masses. The internal mixing between sea-salt particles and inorganic nitrates revealed by individual particle analysis implies that uptake of gaseous HNO3 and/or formation of particulate NO3- through heterogeneous processes occurs on sea-salt particles. A simple uptake model was used to estimate the production rate of particulate NO3- due to these processes. Model calculations showed that the formation of particulate NO3- was mainly due to the uptake of gaseous HNO3 on sea-salt particles in winter Arctic. However, the heterogeneous formation from N2O5 and NO3 also makes an important contribution to the formation of particulate NO3- under no and/or weak solar radiation in winter Arctic (polar night). Thus the heterogeneous formation of NO3- on sea-salt particles may play an important role as a sink of reactive nitrogen oxide in winter Arctic.