AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Source Apportionment and Organic Compound Characterization of Ambient Ultrafine Particulate Matter (PM) in the Los Angeles Basin
SINA HASHEMINASSAB, Nancy Daher, James Schauer, Constantinos Sioutas, University of Southern California
Abstract Number: 214 Working Group: Source Apportionment
Abstract In this study, quasi-UFP (PM$_(0.25), dp<0.25 micro-meter) were collected for 24 hours once per week from April 2008 to March 2009 at 10 different locations in the Los Angeles Basin. Organic constituents of PM$_(0.25) were grouped into polycyclic aromatic hydrocarbon (PAHs), hopanes and steranes, n-alkanes, and levoglucosan, with concentration levels ranging from 0.16-5.5, 0.09-2.2, 9.3-48, and 2.2-106.2 ng m-3 over all sites and seasons, respectively. A molecular marker-based chemical mass balance (MM-CMB) model was applied to estimate the contribution of major sources to PM$_(0.25). The sources included in the MM-CMB model were mobile sources (combined gasoline and diesel vehicles), wood smoke combustion, natural gas combustion, vegetative detritus, and ship emissions. Secondary organic aerosol (SOA) tracers were not included in the model; however their contributions were estimated from non-biomass burning water soluble organic carbon (WSOC$_(nb)) and un-apportioned OC from MM-CMB model (“other OC”). The High correlation (R$^2=0.8) between “other OC” and WSOC$_(nb) in summer suggests that “other OC” is highly impacted by SOA, however un-apportioned primary sources may contribute to “other OC” as well. Mass apportionment results revealed that mobile sources are expectedly the major primary contributors to total quasi-UFP mass, with seasonal average contributions to PM$_(0.25) of 31±12% in summer and 57±17% in winter. “Other organic matter” was the second largest contributor to PM$_(0.25) in all seasons, across the basin, with higher contribution during warmer spring and summer seasons (27%), while lowest during cold seasons (13%). Wood smoke was the third major contributor to PM$_(0.25) in winter, whereas its contribution was lowest in summer. As expected, ship emissions displayed the highest contribution at the near-harbor HUD site, and their levels continually decreased as a function of distance from coast. Lastly, vegetative detritus and natural gas combustion, collectively contributed to 1.3±0.8% of PM$_(0.25) on an annual average basis over all sites.