AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Seasonal and Spatial Variation of Trace Elements and Metals in Quasi-Ultrafine (PM0.25) Particles in the Los Angeles Metropolitan Area and Characterization of Their Sources
ARIAN SAFFARI, Nancy Daher, Martin Shafer, James Schauer, Constantinos Sioutas, University of Southern California
Abstract Number: 239 Working Group: Aerosol Chemistry
Abstract To investigate the variability and sources of trace elements and metals, year-long sampling campaign of quasi-ultrafine particles (PM0.25) was conducted at 10 distinct locations (including source, urban and/or near freeway, rural receptor and desert-like) across the Los Angeles south coast air basin. Time-integrated (24-hour filter-based) samples of aerosols were collected at each site and concentrations of trace elements and metals were quantified using high-resolution inductively coupled plasma sector field mass spectrometry (ICP-SFMS). In order to identify likely sources using elemental grouping information, principal component analysis (PCA) was applied to the dataset. The major sources were identified as road dust, vehicular abrasion, residual oil combustion, cadmium sources and metal plating. These sources accounted for approximately 85% of the total variance of PM0.25 elemental content. Transition metals (such as manganese, iron and cobalt) along with mineral metals (magnesium, calcium, potassium, and sodium, to name a few) were the most important constituents of the first component, originating from road dust, influenced by vehicular emissions as well as resuspended soil. Copper, barium, antimony and molybdenum were the major elements in the second component identified as vehicular abrasion. Tracers of residual oil combustion, including sulfur and vanadium, displayed high loading factors (above 0.8) in the third component and the fourth component was characterized by cadmium as the major element. Finally, nickel and chromium likely associated with metal plating and other industrial activities distinguished the fifth component. Distinct temporal and spatial variations were observed for the identified elemental groups. The concentrations of elements associated with the source and urban locations generally displayed a decline as we proceeded from the coast to the inland. Occasional concentration peaks in the rural receptor sites were also observed, likely driven by the dominant westerly/southwesterly wind transporting the particles to the receptor areas.