Photosensitized reactions as a source of secondary organic aerosols formation in the atmosphere

SSCI-VIDE+CARE+RGM:SPR:CGO:SDUInternational audienceSecondary organic aerosols (SOA) play an important role in air quality. Despite the important number of studies on the formation and aging of SOA, this field remains poorly characterized. It was shown that organic aerosol formation is enhanced by the presence of photosensitizers in aerosols (Aregahegn et al., 2013). Therefore, this study is focused on understanding the photosensitized pathways leading to SOA formation.Different types of photochemical processes can occur upon absorption of UV-Vis light by photosensitizing molecules. When a photosensitizer moves to an excited state, reaction with some surrounding molecules can become possible due to the excess energy. The triplet state lifetime of a photosensitizer is long enough to allow chemical transformation to occur. In this study we are interested in the reactivity of organic photosensitizer in the presence of halide anions (I-; Br-; Cl-). The experimental concept (figure 1) is based laser photolysis coupled to time resolved optical methods to monitor the triplet lifetimes of given photosensitizers in presence of the above mentioned quenchers (in this case halide anions). Four atmospherically interesting molecules and one SOA were studied i.e., xanthone, flavone, acetophenone and oxidized naphthalene. The photosensitizer life obtained and their quenching rate These molecules exhibited interesting chemistry and quenched quite efficiently the halides, leading potentially to various transient species (i.e., radicals). The current status of this innovative research will be presented