利用三维荧光光谱和吸收光谱研究雨水中CDOM的光学特性

Study on Optical Characteristics of Chromophoric Dissolved Organic Matter(CDOM) In Rainwater by Fluorescence Excitation-Emission Matrix and Absorbance Spectroscopy

利用荧光激发-发射矩阵光谱（excitation-emission matrix spectroscopy,EEMs）技术并结合吸收光谱初步研究了2007年厦门梅雨季节期间雨水中有色溶解有机物（CDOM）的光学特性。结果表明,雨水CDOM的吸收光谱随波长呈指数衰减,代表雨水CDOM相对含量的吸收系数a（300）范围在0.27~3.45 m-1,均值为1.08 m-1;且降雨初期CDOM含量高于降雨后期。这表明人类活动和当地的大气污染或空气质量对雨水中CDOM的贡献。雨水CDOM的EEMs光谱揭示出2类4个主要荧光峰（2个类腐殖质荧光A和C与2个类蛋白质荧光B和S）的存在。其中2个类腐殖质荧光A和C之间以及2个类蛋白质荧光B和S之间均存在一定的正相关性,说明其具有相同来源或存在某种内部联系。2个类腐殖质荧光与吸收系数a（300）之间的强正相关性,说明其控制吸收特性的基团可能与控制其荧光特性的基团具有相似性质。结果表明雨水CDOM高吸收和荧光特性在大气化学中的作用不容轻视,在受大气水体影响的太阳辐射的光谱衰减中可能起着潜在的重要作用。

The optical characteristics of chromophoric dissolved organic matter（CDOM） were determined in rain samples collected in Xiamen Island,during a rainy season in 2007,using fluorescence excitation-emission matrix spectroscopy associated with UV-Vis absorbance spectra.Results showed that the absorbance spectra of CDOM in rain samples decreased exponentially with wavelength.The absorbance coefficient at 300 nm [a（300）] ranged from 0.27 to 3.45 m-1,which would be used as an index of CDOM abundance,and the mean value was 1.08 m-1.The content of earlier stage of precipitation events was higher than that of later stage of precipitation events,which implied that anthropogenic sources or atmospheric pollution or air mass types were important contributors to CDOM levels in precipitation.EEMs spectra showed 4 types of fluorescence signals（2 humic-like fluorescence peaks and 2 protein-like fluorescence peaks） in rainwater samples,and there were significant positive correlations of peak A with C and peak B with S,showing their same sources or some relationship of the two humic-like substance and the two protein-like substance.The strong positive correlations of the two humic-like fluorescence peaks with a（300）,suggested that the chromophores responsible for absorbance might be the same as fluorophores responsible for fluorescence.Results showed that the presence of highly absorbing and fluorescing CDOM in rainwater is of significant importance in atmospheric chemistry and might play a previously unrecognized role in the wavelength dependent spectral attenuation of solar radiation by atmospheric waters.