Water-soluble and water-insoluble organic nitrogen in the dry and wet deposition

Abstract

The simultaneous observation of the water-soluble and water-insoluble nitrogen species in the wet deposition, dry deposition, aerosols, and gas phase was conducted for 1 year at an urban site in Japan to clarify the deposition amount and mechanisms of the organic nitrogen species from the atmosphere. The wet deposition amounts of the water-soluble organic nitrogen (WSON) and water-insoluble organic nitrogen (WION) were 0.331 and 0.081 mgN m−2 day−1, respectively, on average, which occupied about 80% and 20% of the organic nitrogen (ON) and about 20% and 5% of the total nitrogen (TN) in the wet deposition, respectively. Organic nitrogen compounds, especially WSON, significantly contributed to the nitrogen deposition through the wet process. The dry deposition amounts of the WSON and WION were 0.042 and 0.050 mgN m−2 day−1, respectively, on average, which occupied about 46% and 54% of the ON and about 28% and 33% of the TN in the dry deposition, respectively. Compared to the wet process, organic nitrogen compounds, especially the WION, more significantly contributed to the nitrogen deposition through the dry process. The dry deposition amount of the WSON and WION contributed about 11% and 38% of their total (wet + dry) deposition, respectively. A significant fraction of the WSON deposition was derived from the dry process, but a large portion of the WSON deposition can be explained by the wet process. A larger contribution of the dry process to the atmospheric deposition was found for the WION deposition, although the wet process was an important deposition pathway even for the WION. The wet deposition amount of the WSON was strongly influenced by the WSON concentration in the rainwater, and would be affected by the uptake of the WSON into the rainwater in the upper atmosphere. The wet deposition amount of the WION was strongly affected by the uptake of the WION in the aerosols with diameters larger than 10 μm (PM>10) in the surface atmosphere. A higher scavenging ratio was found for the WSON than for the WION, which supports these uptake processes. The dry deposition amount of the WSON was affected by the concentration of the gaseous basic WSON, whereas that of the WION was strongly influenced by the WION concentration in the PM>10, which are supported by the measurements of these organic nitrogen species in the aerosols and gas phase and the estimates of their deposition velocities from the resistance model.