Environmental Science and Engineering Seminar
Secondary organic aerosols (SOA) constitute a dominant fraction of ambient fine particulate matter (PM) and have important impacts on climate and health. Photochemical oxidation (OH oxidation in the presence of NOx) and nitrate radical (NO3) oxidations of monoterpenes are important sources of organic nitrates, which have been shown to be ubiquitous in the atmosphere. These reactions represent direct pathways of how anthropogenic emissions mediate and alter aerosol formation from biogenic emissions. In this work, we conduct laboratory experiments in the Georgia Environmental Chamber facility (GTEC) to study the formation and hydrolysis of monoterpene organic nitrates from daytime and nighttime oxidations. Highly oxidized organic nitrates are observed to form rapidly in both gas and particle phases. We systematically investigate the fraction and hydrolysis rate of organic nitrate aerosols. We also synthesize monoterpene hydroxy nitrates and ketone nitrates and study their hydrolysis in bulk solutions at different pH. We find that organic nitrates formed from different oxidation chemistry exhibit different extents of hydrolysis. Further, we demonstrate that organic nitrate hydrolysis is a complex reaction which proceeds via different mechanisms and are controlled by various parameters. Results from these laboratory studies provide the fundamental data for interpreting ambient observations, as well as for chemical transport models to accurately constrain the role of monoterpene organic nitrates with respect to nitrogen budget and formation of ozone and organic aerosols.