Urea in aerosol and rainwater over the East China Sea in winter and spring

Organic nitrogen is a quantitatively important component of fixed nitrogen in atmospheric aerosol and rainwater. Urea as a possible candidate of organic nitrogen component might have a significant influence to the marine ecosystem since its bioavailability and broad range of natural and anthropogenic sources. 23 total suspended particulate samples, 4 size-segregated particles samples and 10 rainwater samples collected over the East China Sea from Nov. to Dec., 2006 and Feb. to Mar., 2007 were applied to analyze the concentrations of urea, nitrate and ammonium in aerosols and rainwater, respectively. In winter and spring, the concentrations of urea nitrogen were from 0.2 nmol · m^-3 to 17.7 nmol · m^-3 and 6.5 nmol · m^-3to 14.6 nmol · m^-3 in bulk aerosols, respectively and the corresponding concentrations were from 7.8 μ mol · L^-1 to 18.1 μ mol · L^-1 and 12.1 μ mol · L^-1 to 35.3 μ mol · L^-1 in rainwater. In both aerosols and rainwater over the East China Sea, the concentrations of urea nitrogen were higher in spring than those in winter. Urea nitrogen in aerosols contributed about 5% to the three measured nitrogen species and it was about 20% in rainwater. The size distribution of urea was markedly different from those of nitrate and ammonium, which had no pronounced difference among cascade stages. A slightly enhance urea contribution presented in the range of 0.43-0.65 μm in spring, which was 19.8%. In contrast, an enhancement presented in the range of 3.3-4.7 pun in winter, which was 19.8%. Factor analysis indicated that the sources of urea in aerosols were dominated by wind-blown soils in winter and sublime of urea in soils in spring, respectively.