CHEMICAL CHARACTERIZATION OF THREE SUMMER CLOUD EPISODES AT WHITEFACE MOUNTAIN

摘要

Cloudwater and aerosol samples were collected during three 1987 summer events at Whiteface Mountain, New York. Dominant inorganic components in cloudwater were SO_4~(2-), NO_3~-, H~+, and NH_4~+. Maximum levels were 978, 256, 421, and 832 μeq 1~(-1), respectively. pH values in cloudwater ranged from 3.1 to 4.4. Large variations in concentrations were found, which can best be explained, on the basis of back-trajectory analysis, by different origins of air masses. A concave concentration versus a time profile for the ionic concentrations was observed, possibly as a result of dilution and concentration as liquid water content changed over the life of the cloud. Dominant components of the aerosol were NH_4~+ and SO_4~(2+);. Changes in the gas-phase concentrations of SO_2, O_3, and H_2O_2 during a cloud event indicated a considerable S(Ⅳ) oxidation potential by H_2O_2. Free acidity (H~+) was 32 - 81% of the total acidity. Carboxylic acid concentrations were dominated by formic acid (13.9 - 39.9 μeq 1~(-1), acetic acid (5.1 - 14.7 μeq 1~(-1), oxalic acid (2.9-19.3 μeq 1~(-1)), malonic acid (3.9-14.7 μeq 1~(-1)), and pyruvic acid (2.4 - 8.6 μeq 1~(-1); these acids have accounted for 7 - 15% of the dissolved organic carbon and up to 22% of the free acidity. Multivariate factor analysis yielded three components that accounted for 91% of the variability of all the parameters: transported acid component, combination of fossil-fuel combustion and automobile emission, and nontransported biogenic component. Primary pollutant concentrations and photochemical activity during long-range transport were the major factors in controlling the chemical species concentrations at the downwind site.