哈尔滨市新降雪中溶解性有机质的光谱特征

Spectroscopic Characterization of Dissolved Organic Matter in Fresh Snow From Harbin

研究新降雪中溶解性有机质(DOM)的光谱特征有利于探究其与大气污染物的响应关系。采用紫外-可见吸收光谱(UV-Vis absorption spectroscopy)、三维荧光光谱(three dimensional fluorescence spectroscopy)结合平行因子分析(PARAFAC)技术,分析了哈尔滨市新降雪样品中DOM的光谱特征及其来源。新降雪中有色溶解性有机质(CDOM)浓度与荧光溶解性有机质(FDOM)强度变化呈现相同趋势,其中CDOM含量因DOM来源、大气云团运移、大气污染情况及发色团光漂白性质的不同而与其他环境介质中CDOM浓度存在差异;而FDOM强度则因环境介质中盐分含量及DOM的降解动力学速率存在差异而小于土壤和海洋。新降雪中DOM的吸收光谱呈现指数递减趋势,与冬季大气颗粒物中水溶性有机物发色团的吸收光谱相似,在200~220 nm处存在明显吸收峰(由于受到水分子和溶解氧影响),表明DOM存在较多的不饱和双键共轭结构。E2/E3值(250和365 nm处的吸光度比值)结果表明,新降雪中DOM具有结构简单、分子量小和芳香性弱的特征,类富里酸为其主要组成物质;通过PARAFAC共解析出类腐殖质和类蛋白质两类荧光组分,其对荧光强度的贡献分别为66.78%和33.22%。荧光参数分析结果表明,该研究新降雪中DOM同时受陆源输入和微生物活动的影响,并且具有较强的自生源特征(BIX>1)和较弱的腐殖化特征(HIX<0.8)。荧光组分与大气污染物的相关性分析表明,哈尔滨市新降雪中的荧光组分具有相同来源,化石燃料、生物质燃烧、交通及工业等排放的细颗粒物(PM2.5)为新降雪中DOM的重要来源,并通过类腐殖质组分的最大荧光强度初步建立了PM2.5浓度值的预测方程。新降雪中DOM光谱特征分析可为揭示其来源组成及深入探寻其载体行为机制提供参考价值,亦可为大气环境污染快速诊断识别提供新的研究思路和技术保障。

The study of the Spectroscopic characterization of dissolved organic matter(DOM)in fresh snow is conducive to exploring its response to atmospheric pollutants.In this research,ultraviolet-visible absorption spectroscopy(UV-Vis)three-dimensional excitation-emission matrix spectroscopy(3DEEMs)combined with parallel factor analysis(PARAFAC)were applied to analyze the spectral characteristics and sources of DOM in fresh snow samples from Harbin.Chromophoric dissolved organic matter(CDOM)content in fresh snow showed the same trend as the intensity of fluorescent dissolved organic matter(FDOM),CDOM content was different from that in other environmental media due to different DOM sources,atmospheric cloud transport,air pollution and chromophore photobleaching properties,however,the intensity of FDOM was lower than that of soil and ocean owing to the differences in salt content and DOM degradation kinetics.The absorption spectroscopy of DOM in the fresh snow showed an exponentially decreasing trend,similar to the absorption spectroscopy of water-soluble organic chromophores in atmospheric particles in winter.Obviously absorption peaks at 200~220 nm(affected by water molecules and dissolved oxygen)indicated that DOM had more unsaturated double-bond conjugated structures.E_(2)/E_(3) values(the ratio of absorbance at 250 and 365 nm)indicated that DOM in fresh snow possessed the characteristics of simple structure,small molecular weight and weak aromaticity.Furthermore fulvic-like acid was the main component of DOM in fresh snow.PARAFAC obtained two types of fluorescent components(humic-like and protein-like),and their contributions to fluorescence intensity were 66.78%and 33.22%,respectively.Fluorescence parameters analysis showed that DOM in fresh snow in the present research was affected by both terrestrial input and microbial activity and had strong autogenic characteristics(BIX>1)and weak humification characteristics(HIX<0.8).The correlation analysis between fluorescence components and atmospheric pollutants revealed that the sources of components of fresh snow in Harbin are similar,the sampling time is during the heating period,and the sampling point is near the factory and the railway.Thus fine particulate matter(PM_(2.5))emitted from fossil fuels,biomass combustion,transportation,and industry were the main sources of DOM in fresh snow.The maximum fluorescence intensity of humic-like components preliminarily established the concentration prediction equation of PM_(2.5).The analysis of DOM spectral characteristics in fresh snow provided a reference value for revealing its source composition and further exploring its carrier behavior mechanism.Meanwhile,it provided a new research idea and technical support for rapid diagnosis and identification of atmospheric environmental pollution.