Contributions of α-Dicarbonyls to Secondary Organic Aerosol Formation From Photo-oxidation of Toluene

Abstract:

Photo-oxidation of toluene leads to significant secondary organic aerosol (SOA) formation, with profound implications for air quality, human health, and climate. This oxidation process yields products with diverse volatility. While the intermediate- to non-volatile oxygenated organics undergo gas-particle partitioning to form SOA, many volatile products are not considered for aerosol formation. Small α-dicarbonyls (e.g., glyoxal and methylglyoxal) are one of the major types of volatile products from toluene oxidation, but their contribution to toluene-derived SOA formation remain elusive. Current experimental results on the multiphase chemistry of α-dicarbonyls are conflicting, casting questions on underlying chemical mechanisms of SOA formation from toluene photo-oxidation. In this study, we performed laboratory measurements by exposing different seed particles to toluene-hydroxy radical oxidation products. SOA formation was characterized by the growth and chemical composition of the particles. Our results indicate that multiphase reactions of α-dicarbonyls play an important role in SOA formation from toluene photo-oxidation, which is larger than the currently recognized.