[Fluorescence Characteristics and Source Analysis of DOM in Snowfall of Xi'an]

Fluorescence characteristics and sources of dissolved organic matter (DOM) in snowfall in Xi'an were studied by three-dimensional fluorescence spectroscopy, parallel factor analysis, and backward trajectory model, which provided a data basis for the analysis of the chemical composition and source of atmospheric organic pollutants. Results show that the DOC content of DOM was 0.88-10.92 mg·L^-1. DOM mainly contained humus-like, fulvic acid-like, tryptophan-like, and tyrosine-like substances. The fluorescence intensity and the summed intensities of these substances exhibited significant positive correlations with the DOC and UV₂₅₄ (P<0.01). The fluorescence index (FI), biological source index (BIX), and humic index (HIX) values of DOM during snowfall were 1.50-1.75, 0.87-1.25, and 1.11-1.97, respectively. FI was positively correlated with BIX and negatively correlated with HIX (P<0.05). During snowfall, the air mass transmission trajectories included the local transmission, long-distance transmission starting from Xinjiang (through Gansu and Ningxia), and medium-distance transmissions starting from Inner Mongolia (through Ningxia) and Shandong (via Henan), accounting for 38.78%, 24.04%, 19.87%, and 17.31% of the total, respectively. This indicates that the content or relative content of the DOM contained in the precipitation can be characterized by fluorescence intensities and their sums of the humic-like, fulvic acid-like, tryptophan-like, and tyrosine-like tyrosine. The DOM in snowfall had both biological and terrestrial characteristics, and belonged to a self-generated source with the newly produced organic matter or matter with stronger self-source characteristics. Local transmission had the most significant contribution to the source of snowfall DOM.