A 50-year record of NOx and SO2 sources in precipitation in the Northern Rocky Mountains, USA

摘要

Ice-core samples from Upper Fremont Glacier (UFG), Wyoming, were used as proxy records for the chemical composition of atmospheric deposition. Results of analysis of the ice-core samples for stable isotopes of nitrogen (δ~(15)N, NO_3~-) and sulfur (δ~(34)S,so_4~(2-) ), as well as NO_3~- and SO_4~(2-) deposition rates from the late-1940s thru the early-1990s, were used to enhance and extend existing National Atmospheric Deposition Program/National Trends Network (NADP/NTN) data in western Wyoming. The most enriched δ~(34)S value in the UFG ice-core samples coincided with snow deposited during the 1980 eruption of Mt. St. Helens, Washington. The remaining δ~(34)S values were similar to the isotopic composition of coal from southern Wyoming. The δ~(15)N values in ice-core samples representing a similar period of snow deposition were negative, ranging from -5.9 to -3.2 ‰ and all fall within the δ~(15)N values expected from vehicle emissions. Ice-core nitrate and sulfate deposition data reflect the sharply increasing U.S. emissions data from 1950 to the mid-1970s.