Concentrations and source insights for trace elements in fine and coarse particulate matter

The Colorado Coarse Rural–Urban Sources and Health (CCRUSH) study is a multi-year study focused on characterizing the mass, composition and sources of coarse particulate matter (PM10−2.5) in Denver and Greeley, CO. Between the two cities, Denver is expected to have greater influence of industry and motor vehicles as sources of PM10–2.5. Greeley is a smaller city with greater expected influence of agricultural activity. As part of the CCRUSH study, we collected integrated 24-h samples of PM from four sites in Denver and Greeley at six day intervals from February 2010 to March 2011. Dichotomous samplers with Teflon filters were used to obtain samples for gravimetric and elemental analysis. Magnetic Sector Inductively Coupled Plasma-Mass Spectroscopy (SF-ICP-MS) was used to analyze digests of monthly composited filter samples for 49 elements. Thirty-nine elements were retained for statistical analysis after excluding those with low signal-to-noise ratios. The elements Sb, Cd, Zn, Mo, As, B, Cu, Pb, and W had crustal enrichment factors greater than 10 in the PM2.5 and PM10–2.5 size ranges in both Denver and Greeley. Using positive matrix factorization (PMF) with bootstrap uncertainty estimation, we identified five factors influencing the element concentrations: a crustal factor contributing to both PM2.5 and PM10–2.5; a sodium-dominated PM10–2.5 factor likely associated with road salt; a vehicle abrasion factor contributing in both size ranges; a regional sulfur factor contributing mainly to PM2.5 and likely associated with coal combustion; and a local catalyst factor identified with high Ce and La enrichment in PM2.5 at one of the sites in Denver.