Indirect photodegradation of anthracene and pyrene induced by dissolved organic matter derived reactive species in ice

Abstract

The influences of dissolved organic matter (DOM) derived reactive species (RS), including singlet oxygen (1O2), hydroxyl radical (•OH) and triplet excited state DOM (3DOM*) on the photodegradation kinetics of polycyclic aromatic hydrocarbons (PAHs) in ice, as well as the spectroscopic changes of PAHs in ice caused by DOM-induced photodegradation were investigated. Anthracene (Ant) and pyrene (Pyr) were chosen as model compounds in this study. The minimum contributions of RS generated from the four DOM to the photodegradation of Ant and Pyr were higher than 20.0 %. •OH contributed more to the photodegradation of Ant and Pyr than 3DOM*. When PAHs coexisted with DOM, direct photodegradation and indirect photodegradation via reaction with 3DOM* seem to have no effect on aliphatic C−C functional groups corresponding to the peak at 1450 cm−1; Photodegradation pathways other than reaction with •OH resulted into the production of C−O functional groups corresponding to the peak at 1113 cm−1; the production of C═O functional groups corresponding to the peak at 1567 cm−1 and the elimination of amide-2 functional groups corresponding to the peak at 1567 cm−1 were attributed to direct photodegradation and indirect photodegradation via reaction with 1O2 and •OH. The fluorescence intensity decreases of Ant when coexisted with DOM were mainly attributed to its direct photodegradation, whereas indirect photodegradation induced by DOM contributed more to fluorescence intensity decreases of Pyr than direct photodegradation.