Estimates of Cloud Water Deposition at Mountain Acid Deposition Program Sites in the Appalachian Mountains

Abstract

Cloud water deposition was estimated at three high-elevation sites in the Appalachian Mountains of the eastern United States (Whiteface Mountain, NY; Whitetop Mountain, VA; and Clingman’s Dome, TN) from 1994 through 1999 as part of the Mountain Acid Deposition Program (MADPro). This paper provides a summary of cloud water chemistry, cloud liquid water content, cloud frequency, estimates of cloud water deposition of sulfur and nitrogen species, and estimates of total deposition of sulfur and nitrogen at these sites. Other cloud studies in the Appalachians and their comparison to MADPro are also summarized. Whiteface Mountain exhibited the lowest mean and median concentrations of sulfur and nitrogen ions in cloud water, while Clingman’s Dome exhibited the highest mean and median concentrations. This geographic gradient is partly an effect of the different meteorological conditions experienced at northern versus southern sites in addition to the difference in pollution content of air masses reaching the sites. All sites measured seasonal cloud water deposition rates of SO₄ ²⁻ greater than 50 kg/ha and NO₃ ⁻ rates of greater than 25 kg/ha. These high-elevation sites experienced additional deposition loading of SO₄ ²⁻ and NO₃ ⁻ on the order of 6–20 times greater compared with lower elevation Clean Air Status and Trends Network (CASTNet) sites. Approximately 80– 90% of this extra loading is from cloud deposition.