AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
SOA from Nitrate Radical Oxidation of Monoterpenes: Effects of Temperature, Humidity, Photochemical Aging on Aerosol Mixing and Evaporation
NGA LEE NG, Christopher Boyd, Theodora Nah, Lu Xu, Georgia Institute of Technology
Abstract Number: 619 Working Group: Effects of NOx and SO2 on BVOC Oxidation and Organic Aerosol Formation
Abstract Secondary organic aerosol (SOA) constitutes a substantial fraction of fine particulate matter and has important impacts on climate and human health. The interactions of biogenic VOCs with NO3 radicals represent a direct way for positively linking anthropogenic and biogenic emissions. Multiple high-time-resolution mass spectrometry organic aerosol measurements were obtained during different seasons at various locations, including urban and rural sites in the greater Atlanta area and Centreville in rural Alabama. Anthropogenic NOx is shown to enhance nighttime SOA formation via nitrate radical oxidation of monoterpenes, resulting in the ubiquitous presence of particulate organic nitrates in the southeastern US. Nighttime NO3 chemistry can contribute up to 22-34% of total measured OA in the southeastern US. Laboratory experiments on nitrate radical oxidation of monoterpenes (a-pinene, b-pinene, limonene) are conducted in the Georgia Tech Environmental Chamber facility (GTEC) to investigate the formation of SOA and fates of organic nitrates under conditions relevant to the southeastern US. A series of experiments is carried out to investigate the changes in aerosol composition and properties during night-to-day transition, where dilution, temperature/RH changes, and photochemical aging take places. Upon photochemical aging, organic nitrates formed from different precursors exhibit drastically different behaviors, suggesting that they can serve as temporary or permanent NOx sinks depending on the monoterpene precursor. Aerosol evaporation is promoted either by isothermal dilution or by increasing the temperature from 25 °C to 40 °C. Results indicate that there is some resistance to aerosol evaporation when temperature is increased. The atmospheric implications of these findings will be discussed.