Seasonal and Spatial Coarse Particle Elemental Concentrations in the Los Angeles Area

The concentrations of trace metals and elements in the coarse fraction of atmospheric particulate matter (CPM, particles smaller than 10 and larger than 2.5 μm in diameter, PM_10–2.5) and their spatial and temporal trends were investigated in the greater Los Angeles area. Ten distinct sampling sites were chosen to encompass a variety of CPM sources, including urban, rural, coastal, inland, and near-freeway sites. Time-integrated 24-h CPM samples were collected at each location once a week, for an entire year, from April 2008 to March 2009, to characterize drivers of the seasonal and spatial patterns of the CPM trace metal content. Metals were quantified using sector-field inductively coupled plasma mass spectrometry (SF-ICP-MS).

Trace metals in CPM displayed distinct seasonal and temporal variations, and a principal component analysis (PCA) was performed to aid the identification of the CPM sources underlying these variations. The probable sources of each principal component were identified using elemental tracers. Major sources of CPM metals and elements identified were crustal and mineral matter, abrasive vehicular emissions, industrial, sea spray, and catalytic converters, explaining more than 80% of the total variance of CPM metal content. Mineral and crustal elements, most notably Fe, Ca, Al, Mg, K, Ti, and Mn, were the main contributors to the overall CPM mass, accounting for over 33% of the total variance, followed by abrasive vehicular markers such as Cu, Ba, and Sb, accounting for over 16% of the variance, with an increasing contribution in the urban sites. Temporal and spatial variations in each identified class of CPM sources were also investigated.