Assessing the Contribution of a-dicarbonyls to Brown Carbon Formation and the Implication for Climate

Brown carbon (BrC) aerosols scatter and absorb solar radiation, directly affecting the Earth’s radiative budget. However, the chemical mechanisms leading to BrC formation is not fully understood, and considerable uncertainties exist in predicting radiative forcing of BrC aerosols in the climate system for current atmospheric models. Small a-dicarbonyls, such as glyoxal, are ubiquitous in the atmosphere, because of significant production from the photooxidation of aromatics from traffic and industrial sources as well as from biogenic isoprene. Current experimental and theoretical results on the roles of a-dicarbonyls oligomerization in BrC and secondary organic aerosol (SOA) formation are conflicting. In this study, we investigated the aqueous reaction of glyoxal by measuring the growth and composition of particles at different pH. Our results indicate that the aqueous reactions of glyoxal provide important sources for BrC and SOA formation and contribute to the aerosol direct and indirect radiative forcing, which are much larger than the currently recognized.