Regional analysis of cloud chemistry at high elevations in the eastern United States

Abstract

Results from the collection and chemical analysis of cloudwater samples collected from May to October 1986–1988 from the five high-elevation ( ⪆950 m MSL ) Mountain Cloud Chemistry Program (MCCP) sites (Whiteface Mountain, NY; Mt Moosilauke, NH; Shenandoah Park, VA; Whitetop Mountain, VA; Mt Mitchell, NC) in the eastern United States are summarized. The resulting database documents the regional chemical climatology of high-elevation forest ecosystems in the eastern U.S. Clouds occured at these sites on 32–77% of the days during the sample collection period. More than 90% of cloud samples were acidic ( prmpH<5.0). The lowest cloudwater pH (2.29 integrated 1-h collection period) was recorded at Mt Mitchell, NC. At all sites sulfate and nitrate were the dominant anions and hydrogen and ammonium were the dominant cations in cloudwater samples. Mount Mitchell received the most acidic clouds and highest chemical exposures, while the Whiteface summit site received the least acidic and lowest chemical exposures compared to other MCCP high-elevation sites. Cloud pH and major chemical components exhibited a seasonal trend with the maxima during the summer months, and correlated well with temperature and ozone concentrations. The mean equivalent ratios of SO 4 2− to NO 3 − were found to be 1.9–3.9 at these sites. It is noted that SO 4 2− correlated highly with hydrogen ion, suggesting that contribution to cloud acidity by sulfate and/or its precursors may be significant.