AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Fine and Ultrafine Particulate Organic Carbon in the Los Angeles Basin: Trends in Sources and Composition
FARIMAH SHIRMOHAMMADI, Sina Hasheminassab, Arian Saffari, James Schauer, Ralph J. Delfino, Constantinos Sioutas, University of Southern California
Abstract Number: 87 Working Group: Source Apportionment
Abstract In this study, PM$_(2.5) and PM$_(0.18) (particles with aerodynamic diameter less than 2.5 and 0.18 micro-meter, respectively) were collected during 2012-2013 in Central Los Angeles (LA) and 2013-2014 in Anaheim. Samples were chemically analyzed for carbonaceous species (elemental and organic carbon) and individual organic compounds. Concentrations of organic compounds were reported and compared with many previous studies in Central LA to quantify the impact of emissions control measurements that have been implemented for vehicular emissions and to provide a current understanding of the sources of carbonaceous aerosols in the LA Basin. A novel hybrid approach of molecular marker-based chemical mass balance (MM-CMB) analysis was conducted, in which a combination of source profiles that were previously obtained from a Positive Matrix Factorization (PMF) model in Central LA, were combined with some traditional source profiles. The model estimated the relative contributions from mobile sources (including gasoline, diesel, and smoking vehicles), wood smoke, primary biogenic sources, and anthropogenic secondary organic carbon (SOC). Mobile sources contributed to 0.65±0.25 micro-gram/m$^3 and 0.32±0.25 micro-gram/m$^3 of PM$_(2.5) OC in Central LA and Anaheim, respectively. Primary biogenic and anthropogenic SOC sources were major contributors to OC concentrations in both size fractions and sites. Un-apportioned OC from MM-CMB (“other OC”) accounted for an average 8.0 and 26 % of PM$_(2.5) OC concentration in Central LA and Anaheim, respectively. A comparison with previous studies in Central LA revealed considerable reduction of EC and OC, along with tracers of mobile sources (e.g. PAHs, hopanes and steranes) as a result of implemented regulations on vehicular emissions. Given the significant reduction of the impacts of mobile sources in the past decade in the LA Basin, the impact of SOC and primary biogenic emissions have a larger relative impact and the new hybrid model allows the impact of these sources to be better quantified.