Dew Chemistry and Acid Deposition in Glendora,California, During the 1986 Carbonaceous Species Methods Comparison Study

Dew was collected and analyzed during the Carbonaceous Species Methods Comparison Study in the Los Angeles basin (Glendora, CA) in August 1986. Formate, acetate, and other carboxylate anions were consistently observed, with formate generally being the most abundant anion in the dew. These carboxylate anions appear to be attributable to deposition of carboxylic acids from the ambient air. Free acid (H⁺) was only about one-fifth of the total dew acidity; carboxylic acids could have accounted for half of the remainder. The H⁺ concentrations were far lower than in dew in the northeast United States (respective pH averages 4.7 and 4.0). Whereas dew in the Northeast was essentially a dilute HNO₃/ H₂SO₄ mixture, that in Glendora contained substantial amounts of many other inorganic species. S(IV) in the dew in Glendora was stable against oxidation, even by H₂O₂, probably signifying formation of the bisulfite adduct with formaldehyde (considerable amounts of formaldehyde and acetaldehyde were present), in contrast to the S(IV) behavior in dew in the Northeast. The Glendora dew results are consistent with 1985 observations in Claremont, 17 km away. Dew appears to play only a minor role in the acid deposition budget in the Los Angeles basin. Daytime dry deposition of HNO₃(g) (and possibly of carboxylic acids) is far more important. In turn, dry deposition appears to be far more important than rainfall in the acid deposition budget of the Los Angeles basin, which yet is probably far smaller per unit surface area than in parts of the Northeast.