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, 1995/19 96 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 a nd Cl-. The number fraction of coarse aerosol particles containing NO3- inc reased in aged oceanic air masses. The internal mixing between sea-salt par ticles and inorganic nitrates revealed by individual particle analysis impl ies that uptake of gaseous HNO3 and/or formation of particulate NO3- throug h heterogeneous processes occurs on sea-salt particles. A simple uptake mod el was used to estimate the production rate of particulate NO3- due to thes e processes. Model calculations showed that the formation of particulate NO 3- was mainly due to the uptake of gaseous HNO3 on sea-salt particles in wi nter Arctic. However, the heterogeneous formation from N2O5 and NO3 also ma kes an important contribution to the formation of particulate NO3- under no and/or weak solar radiation in winter Arctic (polar night). Thus the heter ogeneous formation of NO3- on sea-salt particles may play an important role as a sink of reactive nitrogen oxide in winter Arctic.