AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Wintertime Organic Aerosols in Fresno, California: Characteristics, Sources and Aqueous-phase Processing
XINLEI GE, Ari Setyan, Yele Sun, Qi Zhang, Univeristy of California, Davis
Abstract Number: 331 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract California’s San Joaquin Valley (SJV) suffers from severe aerosol pollution problem, especially during wintertime. Here, we present results on characterization of the organic aerosols (OA) in Fresno, one of the most populated city in this region, during January 2010 using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS). OA dominated the submicron aerosol (PM1) mass, with major contributions from three primary sources – traffic, food cooking, and residential wood combustion. Specifically, traffic-related hydrocarbon-like OA (HOA; O/C=0.09), cooking OA (COA; O/C=0.11), and biomass burning OA (BBOA; O/C=0.33) on average accounted for 22%, 19%, 16% of the OA mass during this study. Primary OA (POA) were particularly prominent during nighttime, contributing up to 80% of the OA mass between 6-9 PM, owing to elevated emissions from evening traffic, dinner cooking and residential heating exacerbated by lower mixed layer height. BBOA correlated best with the polycyclic aromatic hydrocarbons (PAHs) indicating that residential wood burning is a significant source of PAHs. Secondary oxygenated OA aerosol (OOA; O/C=0.42) correlated strongly with both nitrate and sulfate (R>0.84) and accounted for an average 43% of the OA mass. The mass-based size distributions of different OA factors were estimated using a multilinear regression algorithm. Both HOA and BBOA peaked at ~140 nm in vacuum aerodynamic diameter, OOA peaked at ~460 nm, while COA exhibited a unique behavior with two size modes centering at ~200 nm and ~450 nm respectively. Three dense fog events and a persistent rainy period were encountered during this study, allowing us to investigate the effects of aqueous-phase processing on the aerosol chemistry and size distributions. Our results indicate that fog processing enhanced the formation of SOA and other secondary species like sulfate and nitrate. It also shifted the size distributions of secondary species to a larger mode size and enhanced the O/C of SOA.