COMPARISON OF SELENIUM AND SULFUR AT REMOTE SITES THROUGHOUT THE UNITED-STATES

The Interagency Monitoring of Protected Visual Environments (IMPROVE) particulate monitoring network has been collecting aerosols for visibi lity apportionment at remote sites in the United States since 1988. Th e measurements include the major PM(2.5) components, such as sulfur, c arbon, and nitrate, and trace elements, such as selenium. This paper w ill examine the relationship between the sulfurs and selenium concentr ations at 61 sites for samples collected in the seasonal year 1993. Ma ps of mean sulfur and selenium measurements in summer 1993 and winter 1993-1994 indicate that there are well-defined regional patterns for b oth elements, with concentrations in the Appalachian region that are t en times those in areas of the Pacific Northwest. The S/Se ratios of m eans are relatively uniform across the United States, at around 2000 i n summer and 1000 in winter, indicating a strong sulfurselenium relati onship. The role of conversion of SO, to sulfate can also be deduced f rom the means. For individual samples taken during summer 1993, there is a high correlation between the two variables in the East, especiall y at sites in the Northeast, where the correlation coefficients (r(2)) are around 0.9. In the West, the correlation is much lower. This is a ttributed to fewer sources and differing emission factors.