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

Cloud chemical measurements at five elevation (>1,000m MSL) Mountain Cloud Chemistry Program (MCCP) sites in the eastern US for the period from May to October 1986-1988 have been analyzed. Cloud frequency ranged from 32% to 77% of the days at these sites. Greater than 90% of cloud samples at these sites were acidic (pH < 5.0). One extreme sample with pH 2.29 was recorded at Mt. Mitchell. Sulfate and nitrate were the dominant anions in the cloud samples, while hydrogen and ammonium dominated the cations at all sites. Mt. Mitchell received the most acidic clouds and the major chemical exposures, while the Whiteface summit site received the least acidic and 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 month, and correlated well with temperature and ozone concentrations. The mean equivalent ratios of SO double-bond 4 to NO? were found to be 2.0-3.9 at these sites. It is noted that SO double-bond 4 highly correlated with hydrogen ion, indicated that contribution to cloud acidity by sulfate was significant