ANALYSIS AND APPORTIONMENT OF PM_2.5 AND ORGANIC CARBON IN THE UPPER MIDWEST

摘要

Speciated particulate matter less than 2.5 microns (PM_2.5) data collected as part of the Speciation Trends Network (STN) at four sites in the Midwest (Detroit, Michigan; Cincinnati, Ohio; Indianapolis, Indiana; and Northbrook, Illinois) and as part of the Interagency Monitoring of Protected Visual Environments (IMPROVE) program at the rural Bondville, Illinois, site were analyzed to understand sources contributing to organic carbon (OC) and PM_2.5 mass. The U.S. Environmental Protection Agency's (EPA) standalone version of positive matrix factorization (EPA PMF) was applied to data collected from approximately February 2002 through March 2005, and seven to nine factors were identified at each site. Common factors at all sites included mobile with high OC, diesel with high elemental carbon (EC)-to-OC ratio (only at the urban sites), coal combustion, secondary nitrate, soil, and biomass/wood burning. Identified industrial factors included copper smelting (Northbrook, Indianapolis, Bondville), steel (Northbrook), industrial zinc (Northbrook, Cincinnati, Indianapolis), plating with chromium and nickel (Detroit, Indianapolis, Bondville), mixed industrial (Detroit, Cincinnati), and limestone (Bondville). PMF results, on average, accounted for 96% of the measured PM_2.5 mass at each site, residuals were consistently within tolerance (+/-3), and goodness-of-fit (Q) was acceptable. Coal combustion and soil factors showed regional characteristics at each site while industrial sources typically appeared to be locally influenced. These regional factors contributed about one third of the total PM_2.5 mass, on average, while local mobile and industrial sources contributed to the remaining mass. Mobile sources were a major contributor (55% to 76% at the urban sites) to OC mass (OM calculated at 1.8*OC), with generally twice as much mass from non-diesel sources as from diesel. Regional OC associated with coal combustion, biomass burning, and soil was generally low.