Spatial and Temporal Variability of Coarse (PM10−2.5) Particulate Matter Concentrations in the Los Angeles Area

Recent epidemiological and toxicological studies suggest that coarse particulate matter (CPM, particles smaller than 10 and larger than 2.5 μm in diameter, PM 10−2.5 ) concentrations may be associated with adverse health outcomes at levels similar to or larger than those associated with PM 2.5 concentrations. CPM may consist of several, mechanically generated, potentially toxic components, including re-suspended road dust, industrial materials, trace metals, and bio-aerosols. In an effort to better understand and quantify the linkage between sources, composition and the toxicity of coarse PM, 10 sampling sites were set-up in the Los Angeles area. Sites within this diverse monitoring network were selected to encompass urban, rural, coastal, inland, near-freeway, community-based, upwind pollutant “source” and downwind pollutant “receptor” sites to fully characterize the range of likely conditions. At each location, a 24 h time-integrated coarse PM sample was collected once per week for one year in order to assess the seasonal and spatial patterns in coarse PM concentrations. Annual geometric mean CPM mass concentrations varied from <5.0 μg/m 3 to approximately 12 μg/m 3 . Concentrations were 2–4 times higher in the summer than the winter. CPM correlations between sites in close proximity to each other tended to be high (r 2 > 0.80), but were poor between urban center and inland sites. The coefficients of divergence (COD) were also calculated across all site pairs to quantify CPM mass concentration spatial heterogeneity. The CODs (most monthly median values >0.2) suggest modest heterogeneity overall, but the CODs calculated between the urban core site pairs were homogeneous.