AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Measured and Simulated Secondary Organic Aerosol Formation from Vehicle Exhaust in Light and Dark Conditions
YING LI, Yu Morino, Yuji Fujitani, Kei Sato, Satoshi Inomata, Kiyoshi Tanabe, Yoshinori Kondo, Tomoki Nakayama, Akihiro Fushimi, Akinori Takami, Shinji Kobayashi, National Institute for Environmental Studies
Abstract Number: 432 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Secondary organic aerosol (SOA) formed from vehicle exhausts contribute substantially to the atmospheric particulate matter levels in urban air, but are not well represented by current emission inventories or air quality models, due to the uncertainties in SOA formation varied by vehicle types, exhaust aftertreatment devices and oxidation conditions. In this work, smog chamber experiments were conducted to investigate the SOA formation from dilute emissions from two light-duty gasoline vehicles, one light-duty and one medium-duty diesel vehicles. Emissions were oxidatively aged in the smog chamber for a variety of dark (i.e., O3) and UV (i.e., OH) conditions. Substantial SOA formation was observed in all UV and dark aging experiments. The predictions of a volatility basis-set model were compared with the measurements from an aerosol mass spectrometer. The model predicted that the intermediate-volatility organic compounds (IVOC) played an important role in the diesel SOA formation, contributing more than 80% of the simulated concentrations. Inclusion of the unspeciated IVOC in the model improved the simulations but the model still underpredicted the observed diesel SOA concentrations in the dark experiments. The model could not reproduce the rapid burst of SOA production that occurred in the early phase of aging, especially for the dark ozonolysis experiments. OA formed from gasoline vehicles have higher O:C comparing to diesel vehicles. The ageing scheme applied in this study reproduced the measured O:C reasonably well for the light experiments. The model underestimated the O:C of gasoline OA and overestimated the O:C of diesel OA in the dark experiments. Future experiments characterizing the existence of organic nitrate (ON) and including explicit formation pathway of ON in models may improve the discrepancy between simulated and observed SOA concentration and oxidation state in dark conditions.