Distribution Of Dissolved Organic Nitrogen In Atmospheric Aerosols At The Coastal Area Of Qingdao

Organic nitrogen is an important component of nitrogen-containing compounds in atmospheric aerosols, and might have a significant influence on the nutrition budgets of marine ecosystem and the global nitrogen cycling. In the previous studies, most nitrogen budgets have focused on inorganic nitrogen, while possible contribution of an organic component has been ignored. So the atmospheric deposition budgets based solely on inorganic nitrogen are likely to be underestimating the ecological effect of the atmospheric nitrogen deposition on the marginal seas of China. Organic nitrogen compounds have various forms in atmospheric aerosols, amino acids and urea are the interesting compounds of which because of the bioavailability of these compounds in deposition and their potential roles in ecological processes and plant nutrition. The studies of organic nitrogen, amino acids and urea in the atmospheric aerosols would be helpful to evaluate the roles of organic nitrogen in the global atmospheric nitrogen budget and marine ecosystem.The overall goal of this paper was to characterize total dissolved organic nitrogen , free amino acids and urea in total suspended particles, TSP and size-segregated particles from the coastal area of Qingdao in order to understand the effects of organic nitrogen on the marine ecosystem. The major results were reported here including the concentrations, seasonal variations and distributions of dissolved organic nitrogen, free amino acids and urea in 83 TSP samples and 47 series anderson size-segregated samples collected from December 2004 to February 2005,July 2005 to August 2006 at the coastal area of Qingdao.The conclusions were summarized as follow:The average concentration of DON in TSP in Qingdao was 190±100n molNm-3,accounted for 20.8±6.2% of TN. Concentrations of DON exhibited less pronounced seasonal trend, with higher values occurring during Nov., Dec. and Mar. and a factor of～6 difference in the minimum and maximum values. The annual average concentration of free amino acids nitrogen(FAA-N)was 808.3±417.4 pmolNm-3, only accounted for < 1% of DON. Concentrations of FAA-N varied seasonally, with peaks during spring and autumn. Arg,Gly,Thr,Tyr,Ala and Orn were the dominant FAA species, together accounting for more than 70% of the total FAA-N pool in aerosols. Urea nitrogen concentration ranged from 0.43nmolNm-3 to 5.09 nmolNm-3, and represented <3% of the total organic nitrogen. Concentrations of urea nitrogen peaked during spring and summer.The mass distribution on different size fraction of aerosols showed that particle mass was dominated by the fine particles with diameter less than 2.1μm. About 60% of particles were found in fine particles during the summer. In spring and autumn, larger particles tend to have higher mass concentrations. Bimodal particle size distributions have been observed in the winter, with maxima around 3.3-4.7μm and 0.43-0.65μm. The size distribution of DON in summer was complex, but in the other seasons unimodal distributions of DON were obtained and about 70% of DON occurred in the particles of diameter less than 2.1μm. The size distributions of amino acids nitrogen have less pronounced peaks. The percentage of FAA-N to the total amino acids in fine particles was similar to that in coarse particles, and about 85% of FAA-N was found in PM₁₁ particles. Urea size distribution showed the bimodal distributions with maxima around 0.65～1.1μm and 7.0～11μm. About 69% of urea nitrogen was found in fine particles.