不同分子尺寸溶解性有机物的光解行为研究

Photochemical Degradation of the Size-Fractionated Dissolved Organic Matter

研究了三个分子量区间(0.45μm^100kDa,100~5kDa和<5kDa)的溶解性有机物(DOM)在不同光源辐照下的光解行为。溶解有机碳(DOC)和UV254的测试结果表明,光解可以有效地减少所有分子量区间的DOM总量,而且UVC光源的存在可以进一步促进DOM的降解。三维荧光光谱测定结合平行因子分析,识别出3个腐殖质类荧光组分(C1:UVA+UVC,C2:UVA+UVB,C3:UVC)。在光解过程中,较大分子腐殖质类(>5kDa)的荧光强度相对较稳定,甚至增强;而小分子腐殖质类(<5kDa)的荧光组分C1和C2具有显著的光解行为,UVC的存在可以促进两种荧光组分的光解。所有分子量区间的C3组分都发生了光生成现象。

In this study,the photo degradation of the size-fractionated（ 0. 45μm-100kDa,100kDa-5kDa, 5kDa） dissolved organic matter（ DOM） at different light sources was investigated. Measurements of dissolved organic carbon（ DOC） and UV254 absorbance showed that sunlight exposure led to the decrease of DOM in all the three fractions over a 6-days period of 6 h/d irradiation,and the presence of UVC light in natural sunlight can speedup DOM elimination. The parallel factor（ PARAFAC） analysis of fluorescence excitation emission matrices（ EEM） revealed the presence of three humic-like components（ C1： UVA ＋ UVC; C2： UVA ＋ UVB; C3： UVC） in the DOM samples. In addition,the fluorescent components in large-size DOM fractions（ 5kDa） were not sensitive to sunlight exposure,and some of which increased upon sunlight exposure. However,the C1 and C2 in the small-size DOM fractions（ 5kDa） were much more susceptible to sunlight exposure,both of which decreased significantly after the 6-days incubation. But,the C3 components in all DOM fractions were found to be photo-produced. Also,the presence of the UVC light in sunlight can somewhat speedup the elimination of C1 and C2 or decrease the generation of C3.