TRENDS IN ELEMENTAL CONCENTRATIONS OF FINE PARTICLES AT REMOTE SITES IN THE UNITED-STATES-OF-AMERICA

The University of California at Davis has been monitoring particulate concentrations in remote sites throughout the United States of America since 1979 in networks operated for the National Park Service and the Environmental Protection Agency. Twelve sites in remote class I visibility areas have almost complete records from June 1982 to August 1992, seven in the southwest, three in the northwest, and two in the east. During this period, two samples of fine particles (0-2.5 mum) on Teflon filters were collected every week and analysed for elemental concentration by Particle Induced X-ray Emission (PIXE). This paper will examine the historical trends for sulfur, zinc, lead, and the soil elements. Measurements during the past four years have verified that the sulfur is present as sulfate. In the southwest, 80% of the sulfur trends in spring, summer and fall decreased, while most of the winter trends increased. The annual trends decreased at six of the seven sites. The trends in the northwest increased slightly. The two eastern sites had the most important trends, with significant increases of almost 4% per year in summer, 1-3% increases in spring and fall, and 2% decreases in winter. The annual increases were between 2 and 3%. Generally there were no significant trends for zinc and the soil elements. Lead at all sites decreased sharply through 1986, corresponding to the shift to unleaded gasoline, but has since leveled off at around 18% of the 1982 means. The most important conclusion of this study is that through the use of stable sampling and analytical protocols, we have been able to determine statistically significant historical trends of as small as 1-2% per year for sites with 10-year records.