10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Secondary Organic Aerosol Production over Seoul, South Korea, during KORUS-AQ
BENJAMIN A. NAULT, Pedro Campuzano-Jost, Douglas Day, Jason Schroder, Bruce Anderson, Andreas Beyersdorf, Donald Blake, William Brune, John Crounse, Ronald Cohen, Joost de Gouw, Jack Dibb, Josh DiGangi, Glenn Diskin, Alan Fried, Greg Huey, Christoph Knote, Kara D. Lamb, Taehyoung Lee, Sally Pusede, Joshua P. Schwarz, Paul Wennberg, Armin Wisthaler, Jose-Luis Jimenez, et al., University of Colorado-Boulder
Abstract Number: 546 Working Group: Air Quality in Megacities: from Sources to Control
Abstract Secondary organic aerosol (SOA) is rapidly produced over and downwind of urban areas, causing important effects on health, visibility, and climate. At this time, only a few megacities have been well characterized for urban SOA production. In this study, we utilize observations from the NASA DC-8 over Seoul, South Korea, during the NASA/NIER 2016 KORean United States-Air Quality (KORUS-AQ) study to quantitatively investigate the relative importance of transported OA (and SOA precursors) to Seoul versus the influence of local emissions of SOA precursors.
From the airborne observations, we find that SOA production (normalized to excess CO) over Seoul is higher than that observed over other urban areas around the world, including even locations in China. However, when SOA production is normalized to excess CO2, the SOA production across urban areas shows more similarity, due to China having higher CO emissions relative to SOA precursor than other areas. Results from an Oxidation Flow Reactor (OFR), that was flown on the NASA DC-8, shows that the absolute potential SOA over Seoul is a factor of 3 higher than over the West Sea, indicating local emissions are dominating the SOA production over this urban region, similar to results for more isolated urban regions like Los Angeles and Mexico City. Also, we find that the potential SOA produced in the OFR during morning overpasses of the city are similar to the observed ambient SOA produced later in the day, indicative of photochemistry dominating the SOA production over this urban region. Furthermore, correlations of SOA with short-lived products (formaldehyde and peroxy acyl nitrate, which have lifetimes of less than 4 hours in this region) from oxidation of hydrocarbons, along with correlation of SOA with ozone, indicate that the SOA is being locally produced from photochemistry of local hydrocarbon emissions. We corroborate this finding through calculations of potential SOA productions from observations, finding that short-lived hydrocarbons (OH chemical lifetimes of less than 1 day) dominate (~90%) the SOA production budget. Finally, local dominance of SOA precursors is further supported with source analysis results from WRF-Chem / FLEXPART, using NO2 as a surrogate for short-lived hydrocarbons (given their similar lifetimes). This study highlights the role of local hydrocarbon emissions with rapid photochemistry dominating the SOA production budget in the Seoul urban region.