Occurrence of water soluble organic nitrogen in aerosols at a coastal area

Aerosol samples (205) were collected from January 2005 to November 2006 at a coastal site at Keelung City (Taiwan), on the southern East China Sea. The atmospheric concentrations of major ions indicated that the area was dominated by different air masses at different times of the year: continental Asia from January to May and November to December; air masses from Indonesia and surrounding islands (south-eastern region) dominated during early-summer (July 2005 and June 2006), and air masses directly from the adjacent ocean dominated during late-summer (July to August 2006) and early-autumn (September to October 2005). The atmospheric concentrations of water soluble organic nitrogen (WSON) corresponded to the different sources and weather conditions. The results of a factor analysis of combined major ions, water soluble inorganic nitrogen (WSIN) and WSON indicated that a fossil fuel combustion source and biomass burning were the two major controlling factors during the sampling period. We discuss the correlations between WSON, WSIN and major anthropogenic ions in relation to the different formation mechanisms for the various sources. We propose a mechanism whereby biomass burning is the major input of aerosols derived from mainland China. Fossil fuel combustion was found to be important during periods when aerosols were derived from the south-eastern area. Our data indicate that WSON was predominantly associated with aerosols derived from biomass burning when the origin of the air mass was mainland China.