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

Abstract

Atmospheric aerosol particles and acidic gases were collected at Ny‐Ålesund, 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 oxides. Atmospheric inorganic nitrates were mostly present as particulate NO3− in the coarse mode defined as diameter >2.3 μm) of which major constituents were sea‐salt compounds such as Na+ 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.