大气有机氮沉降研究进展

Atmospheric deposition of organic nitrogen:A review

大气氮素沉降是全球氮素生物地球化学循环的一个重要部分,包括干?湿沉降两种,以无机态和有机态形式发生沉降。长期以来由于受研究方法的限制,国际上对大气氮素沉降的研究多集中在无机态氮的沉降上,忽视了对有机态氮形式发生的沉降,因而造成了人们对大气氮素沉降总量的低估。在全面总结国内外文献的基础上,综述了大气有机态氮沉降的研究进展,具体包括大气有机氮的来源、种类?雨水有机氮的测定方法?有机氮沉降对大气氮沉降总量(氮沉降总量=无机氮沉降+有机氮沉降)的贡献,以及有机氮沉降可能的生态效应等。最后,指出了今后我国大气有机氮沉降研究需要加强的主要方面。

This paper reviews the recent literature on atmospheric deposition of organic nitrogen （ N ）. Atmospheric N deposition includes both wet and dry deposition of inorganic and organic forms of N and is an important part of the global biogeochemical N cycle. Organic forms of N are widespread in the atmosphere and their deposition may contribute substantially to N inputs into terrestrial and aquatic ecosystems. Most evaluations of atmospheric N deposition have focused exclusiyely on the deposition of inorganic N forms, mainly NH4-N and NO：N. Organic N deposition, however, has received scant attention and has often been assumed to be negligible because of methodological problems, with the result that total atmospheric N deposition fluxes have often been underestimated. Recent research on NADP （ National atmospheric deposition program） precipitation samples indicates that up to 30% of atmospheric N deposition may be due to organic N. Our initial results indicate that the contribution of organic N to total N in precipitation was up to 22% in the Beijing area in the late 1990＇s. Possible sources of atmospheric organic N include direct emissions of natural and anthropogenic organic N, bacteria and pollen in the air, and byproducts of reactions between NO, and hydrocarbons. The information currently available indicates that organic N in atmospheric deposition comprises numerous individual compounds including urea, amine acids and PAN. Conceptually, the substances involved can be divided into three major classes ： organic nitrates （ like PAN）, reduced atmospheric N and primary biological materials. However, few studies have attempted to comprehensively identify individual constituents of organic N in precipitation or aerosol samples. At present the magnitude of atmospheric organic N deposition has been measured mainly as wet deposition, and little is known about the dry deposition. The most widely employed methods for quantifying organic N in precipitation are Kjeldahl digestion, persulfate wet oxidation, UV photo-oxidation, high-temperature combustion and mass spectrometry. In the first four techniques, organic N is inferred from the difference between total N and inorganic N measured in sample splits. The percentage contribution of organic N to total N loading varies from site to site, and different measurement techniques among different groups also contribute to variability in the results, but values are consistently around 10% to 40%. Preliminary estimates of the magnitude of the global atmospheric organic N fluxes are between 10Tg N and 50 Tg N per ecologically important. Finally, the paper stresses the importance of year, and the atmospheric organic N flux may be expanding the range of studies on atmospheric deposition of organic N in China.