Effect of sunlight irradiation on fluorescence properties of dissolved organic matter

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 irradiation. The initial 3DEEM of Fluka HA had only one fluorescence peak at lambda(ex)/lambda(em) = 275/500 nm, while two fluorescence peaks occurred at lambda(ex)/lambda(em) =245/450 nm and 310/450 nm, respectively, after sunlight irradiation. lambda(ex) and lambda(em) 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.