Cloud deposition, high-elevation sites

Fig. 16-4 pH sensitivity to SO4- and NH4. Model calculations of expected pH of cloud water or rainwater for cloud liquid water content of 0.5 g/m. 100 pptv SO2, 330 ppmv CO2, and NO3. The abscissa shows the assumed input of aerosol sulfate in fig/m and the ordinate shows the calculated equilibrium pH. Each line corresponds to the indicated amoimt of total NH3 + NH4 in imits of fig/m of cloudy air. Solid lines are at 278 K, dashed ones are at 298 K. The familiar shape of titration curves is evident, with a steep drop in pH as the anion concentration increases due to increased input of H2SO4. (From Charlson, R. J., C. H. Twohy and P. K. Quinn, Physical Influences of Altitude on the Chemical Properties of Clouds and of Water Deposited from the Atmosphere." NATO Advanced Research Workshop Acid Deposition Processes at High Elevation Sites, Sept. 1986. Edinburgh, Scotland.)... 

In addition to wet and dry deposition, many high-elevation sites may receive substantial inputs of N from clouds or fog (15-17). Few quantitative estimates of cloud deposition are available, but results from one site on Whiteface Mountain in the Adirondacks indicate that clouds and fog can contribute up to 40% of total deposition (18). Rates of wet and dry deposition at Whiteface Mountain were comparable to the Adirondack values given in Table I ( 740 equiv/ha), but total deposition rates (including cloud and fog deposition) averaged 1170 equiv/ha. 

Herckes, P., Mirabel, P., Wortham, H. 2002. Cloud water deposition at a high elevation site in the Vosges Mountains (Franee). Sei. Total Environ. 296 59-75. 

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