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CLOUD CHEMISTRY IN THE EASTERN UNITED STATES, AS SAMPLED FROM THREE HIGH-ELEVATION SITES ALONG THE APPALACHIAN MOUNTAINS
Citation:
Anderson, J. B., R E. Baumgardner, J. Bowser, AND V. A. Mohnen. CLOUD CHEMISTRY IN THE EASTERN UNITED STATES, AS SAMPLED FROM THREE HIGH-ELEVATION SITES ALONG THE APPALACHIAN MOUNTAINS. ATMOSPHERIC ENVIRONMENT 33:5105-5114, (1999).
Impact/Purpose:
Our main objective is to assess the exposure of selected ecosystems to specific atmospheric stressors. More precisely, we will analyze and interpret environmental quality (primarily atmospheric) data to document observable changes in environmental stressors that may be associated with legislatively-mandated emissions reductions.
Description:
Atmospheric deposition of acidic cloud water is thought to be one of the causes for the recent forest decline in industrialized areas of the world. The present paper presents results from the Mountain Acid Deposition Program (MADPro), a part of EPA's Clean Air Status and Trends Network, (CASTNet). We used automated cloud water collectors at three selected mountain sites (Whiteface Mt., NY; Whitetop Mt., VA; and Clingman's Dome,TN) to take hourly samples from non-precipitating clouds during temperature (non-freezing) seasons of each year from 1994 to 1997. Samples were promptly analyzed for pH, conductivity, and concentration of dissolved ions. Cloud liquid water content (LWC) and meteorological parameters were measured at each site. Mean cloud frequencies and LWC of clouds were higher at Whiteface Mt., NY, than in the Southern Appalachians. The four most prevalent ions found in cloud water samples were usually, in order of decreasing concentration: sulfate (SO42-) hydrogen (H+), ammonium (NH4+), and nitrate (NO3~). Within cloud events the concentration of these major ions tended to co-vary. Typically there was an inverse relationship between LWC of the cloud and ionic concentration of the cloud water. During the sampling season, the highest ionic concentrations were seen during mid-summer. Ionic concentration of samples from the southern sites were significantly higher than samples from Whiteface Mt., but further analysis indicates that this is a least partially due to the north-south difference in the LWC of clouds. MADPro results are shown to be comparable with previous studies of cloud chemistry in North America.