10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Quantification of the Rapid Photochemical Secondary Organic Aerosol Production Observed across Megacities around the World
BENJAMIN A. NAULT, Pedro Campuzano-Jost, Douglas Day, Jason Schroder, Donald Blake, Manjula Canagaratna, Joost de Gouw, Jessica Gilman, Tom Hanisco, Greg Huey, B. Thomas Jobson, Bill Kuster, Barry Lefer, Jin Liao, Ilana Pollack, Jeff Peischl, James Roberts, Thomas Ryerson, Alan Fried, Bernhard Rappenglueck, Jochen Stutz, Petter Weibring, Frank Flocke, Jose-Luis Jimenez, et al., University of Colorado-Boulder
Abstract Number: 544 Working Group: Air Quality in Megacities: from Sources to Control
Abstract Organic aerosol (OA) is an important fraction of the submicron aerosol budget over urban areas around the world, with substantial and rapid secondary OA (SOA) production observed in all megacities studied to date. However, multiple studies over different megacities have shown that SOA formation cannot be accounted for when only considering traditional volatile precursor compounds (e.g., aromatics). Either other sources of SOA, including semi-volatile and intermediate-volatility anthropogenic volatile compounds (S/IVOCs) and glyoxal uptake, or much higher SOA yields for the VOC precursors are needed to account for the observed urban SOA production. Models including S/IVOCs have shown the most success in capturing the SOA production in megacities.
Using data from major megacities (Houston, 2000 and 2013, Mexico City, Los Angeles, Beijing, and Seoul) around the world, we further explore the photochemical aspects and the importance of S/IVOCs to urban SOA production. With these data, we find differences in the emission normalized SOA production for these cities that are remarkably consistent with differences in the slopes of SOA versus various other secondary photochemical species (ozone, formaldehyde, and peroxy acyl nitrate). We found that these can be explained by the differences in the mixtures of hydrocarbons emitted in the different cities. In megacities, when aromatics are more important, the hydrocarbon mixture is more efficient, per OH molecule reacted, in producing SOA, relative to the gas-phase photochemical products; whereas, when small alkenes are more important, the opposite is true. We show that this relationship has a very strong linear relationship across megacities around the world. We also discuss how the slopes between OOA and secondary photochemical species not only demonstrate that photochemical production of SOA dominates the OA budget over megacities, but how these slopes provide insight into the effective SOA yield from the hydrocarbon emissions in an urban area. The effective SOA yields from these slopes further suggest the importance of S/IVOCs to explain the observed SOA over megacities. The results from this study will allow improved quantification of urban SOA production and more accurate predictions in chemical transport models.