Triplet-State Organic Matter in Atmospheric Aerosols: Formation Characteristics and Potential Effects on Aerosol Aging

Abstract Triplet-state organic matter could be generated by chromophoric organic aerosols under light exposure, which furtherly induce aerosol aging. The characteristics of triplet-state generation have not been fully investigated to date in organic aerosols. Here, we conduct a comprehensive investigation of the generation characteristics of triplet-state chromophoric dissolved organic matter (3CDOM*) in primary, secondary and ambient aerosols. The results show that biomass combustion have the strongest capacity of 3CDOM* generation, while vehicle emissions are the weakest. In ambient aerosol, there is a stronger ability to generate 3CDOM* in winter than in summer. The various types of CDOM are identified by the EEM-PARAFAC method, and the structure-activity relationship between the type of CDOM and the capacity of 3CDOM* generation is investigated. The results show that two types of CDOM, which are usually identified as N-containing substances, contributed 88% to triplet-state generation. According to the spin trapping and electron paramagnetic resonance technique, we estimate that 3CDOM* induce at least 30% of the singlet oxygen (1O2) and 31% of the hydroxyl radical (•OH) in aerosols. The estimated generation rate of 3CDOM* reached ~100 μmol m−3 h−1 in the atmosphere in Xi'an, China, which is approximately one hundred thousand times that of •OH. These results indicate that 3CDOM* is likely a significant contributor to aerosol aging in the actual atmosphere.