Characterization of carbonaceous matter from the USEPA coarse PM pilot speciation study

One year of nominally 1-in-6 day dichot PM samples collected in Phoenix and East St. Louis were analyzed for EC and OC using the IMPROVE-A method. Study-average OC concentrations were higher in the fine fraction than the coarse fraction at both sites. The coarse fraction exhibited relatively lower abundance of the more volatile fractions (OC1, OC2) and relatively higher abundance of the less volatile fractions (OC3, 0C4). The distribution of OC across the TOA fractions for coarse PM was nearly identical for the two sites. More work is needed to evaluate whether this is merely coincidental or reflects similar sources of coarse organic carbonaceous matter. OC was ∼50% higher on quartz-behind-Teflon filters than quartz-behind-quartz filters. This observation is consistent with the literature which generally recommends the quartz-behind-Teflon configuration as the preferred estimate of the organic vapor artifact¹³. However, the backup filter OC mass loadings were greater for the major flow samples compared to the minor flow samples despite the major flowing having a face velocity that is only 11% of the minor flow face velocity. This pattern might arise from equilibrium never being reached between the minor flow channel backup filter and the gas phase organic vapors. Results from biological content analyses and organics speciation will also be included in the presentation.