太阳辐射对溶解有机质荧光光谱特征的影响

Effect of Sunlight Irradiation on Fluorescence Properties of Dissolved Organic Matter

利用三维荧光光谱研究了太阳辐射对溶解有机质(DOM)荧光光谱特征的影响。实验结果表明,太阳辐射使DOM的荧光发射光谱强度减弱。在三维荧光光谱图中,红枫湖样品的荧光峰A,C,南明河样品的荧光峰A,B,C,尤其是荧光峰C的λExmax/λEmmax位置随着太阳辐射时间的延长而逐渐向短波长移动。从腐殖酸样品的三维荧光光谱图中则发现,原始样品荧光峰位置出现在λEx/λEm=275/500nm处,光照作用后出现两个荧光峰λEx/λEm=245/450nm和310/450nm。太阳辐射对DOM中不同荧光组分的光降解速率存在差异,从荧光峰A和C的比值r(A,C)随太阳辐射时间的变化趋势得知,荧光峰C比荧光峰A的荧光丢失速率更大,即对于太阳辐射作用更敏感。在整个光降解过程中,红枫湖、南明河DOM的r(A,C)值比标准腐殖酸Fluka HA的r(A,C)值的变化更显著。通过本研究表明,可以利用三维荧光光谱所提供的完整的光谱信息来研究DOM在光降解过程中的光谱特征以及物理化学组成等变化。

Three-dimensional excitation emission matrix fluorescence spectroscopy （3DEEM） was used to investigate the effect of sunlight irradiation on the fluorescence properties of dissolved organic matter （DOM） from Lake Hongfeng and Nanming River waters and a commercial fluka humic acid （FHA）. The results show that the DOM samples and FHA fluorescence properties changed under sunlight irradiation. Interestingly, the photodegradation characteristics were different between aquatic DOM and FHA. The fluorescence intensity of the apparent peaks A, B and C of lake and river water DOM decreased with sunlight irradia tion. The initial 3DEEM of Fluka HA had only one fluorescence peak at λex/λem = Z75/500 nm, while two fluorescence peaks occurred at λex/λem =245/450 nm and 310/450 nm, respectively, after sunlight irradiation. λex and λem maxima of DOM decreased during 7 days of sunlight irradiation. Changes in r（A, C） of DOM and FHA with sunlight irradiation time suggest that fluorescence peaks A and C had different fluorescence loss rates, while peak C fluorophores were more susceptible to sunlight irradiation. FHA appeared to be less susceptible to photodegradation, and its r（A, C） remained almost the same before and after sunlight irradiation.