Seasonal and spatial variations of sources of fine and quasi-ultrafine particulate matter in neighborhoods near the Los Angeles–Long Beach harbor

Abstract

The Los Angeles–Long Beach harbor is the busiest port in the US. Levels of particulate matter (PM) are relatively high in this area, since it is affected by multiple PM sources. A Chemical Mass Balance (CMB) model was applied to speciated chemical measurements of quasi-ultrafine and fine particulate matter from seven different sites. Winter measurements were obtained during a 7-week period between March and May 2007, and summer measurements corresponded to a 6-week period between July and September 2007. Four of the sites were located within the communities of Wilmington and Long Beach, two sites were located at a background area in the harbor of Los Angeles and Long Beach, and one more site was located further downwind, near downtown Los Angeles, representing urban downtown LA, influenced by mostly traffic sources. The samples were analyzed for organic (OC) and elemental (EC) carbon content, organic species, inorganic ions, water soluble and total elements. The sources included in the CMB model were light duty vehicles (LDV), heavy-duty vehicles (HDV), road dust (RD), biomass burning and ship emissions. The model predictions of the LDV and HDV source contributions accounted, on average, for 83% of total fine OC in winter and for 70% in summer, whereas ship emissions’ contribution was lower than 5% of total OC at all sites. In the quasi-ultrafine mode, the vehicular sources accounted for 118% in winter and 103% in summer. Spatial variation of source contributions was not very pronounced with the exception of some specific sites. In terms of total fine PM, vehicular sources together with road dust explain up to 54% of the mass, whereas ship contribution is lower than 5% of total fine PM mass. Our results clearly indicate that, although ship emissions can be significant, PM emissions in the area of the largest US harbor are dominated by vehicular sources.