Source apportionment of benzene downwind of a major point source

In the United States, the Emergency Planning and Community Right–to–Know Act requires sources that emit more than their Threshold Planning Quantity (TPQ) must publically report their total annual emissions. Because these values are aggregated over an entire year, high total emissions are often reported in the toxic release inventory. The Akwesasne Mohawk Reservation in rural Northern New York State lies downwind of an industrial source that reported annual benzene emissions of approximately 29 000 pounds. To assess if these emissions contributed significantly to the ambient concentrations, 24 hour canister samples were collected every 6th day from May 30 2007 to July 12 2008 at 9 locations on the Reservation. The samples were analyzed for benzene, toluene, ethyl benzene, and xylenes (BTEX) by GC/FID/MS using EPA Method TO15 procedures. In addition, gasoline samples (6 regular unleaded, 2 midgrade unleaded and 2 super unleaded) were collected in December 2007, May 2008 and July 2008 from five gas stations. The concentrations of BTEX in each gasoline sample were determined by headspace analysis. Vehicle tailpipe sampling was conducted by directly collecting samples from the tailpipe into Tedlar bags on 5 days: March 26, 2008, April 24, 2008, May 8, 2008, May 29, 2008 and June 12, 2008. Three samples were collected from each of the 22 vehicles that were fueled with unleaded regular gasoline from the reservation. Using these measured source profiles and ambient concentrations, the Chemical Mass Balance model was applied to each sample to assess the source contributions of BTEX. The results show that the predominant benzene source is vehicular exhaust with a small contribution from gasoline volatilization. The industrial plant has little or no impact on the ambient benzene concentrations in this community.