Attribution of particulate sulfur in the Grand Canyon to specific point sources using tracer-aerosol gradient interpretive technique (TAGIT)

Since aerosol particulate sulfur is generally a secondary airborne pollutan t, most source attribution techniques require many assumptions about the tr ansport and chemistry of sulfur dioxide (SO2) emissions. Uncertainties in o ur understanding of these processes impair our ability to generate reliable attribution information that is necessary for designing cost-effective pol lution control policies. A new attribution technique using artificial trace r is presented in hopes of reducing the uncertainty of secondary aerosol so urce attribution. The Tracer-Aerosol Gradient interpretive Technique (TAGIT ) uses tracer data from a monitoring network to distinguish sites impacted by a source tagged with tracer from nonimpacted sites. Sites determined not to be influenced by the plume are considered to represent background parti culate sulfur concentrations. The particulate sulfur attributable to the so urce at sites within the plume is calculated as the difference between obse rved and background particulate sulfur TAGIT is applied to measurements mad e in the vicinity of the east and west ends of the Grand Canyon in order to attribute particulate sulfur to the sources within the Eastern Colorado Ri ver Valley (ECRV) and the Mohave Power Project (MPP), respectively. TAGIT r esults indicate that during the winter intensive field sampling experiment (January 15-February 13, 1992), an average of 59 +/- 12% of the particulate sulfur at Marble Canyon, AZ, was attributable to ECRV sources. Similarly d uring the summer field sampling experiment (July 13-August 30, 1992), MPP i s estimated to have contributed an average of 7 +/- 3% of the particulate s ulfur at Meadview, AZ. Uncertainties associated with the assumptions of TAG IT are discussed and quantified. The attribution results suggest that SO2-t o-sulfate conversion rates are highly variable from day to day in this regi on.