Characterization of organic acids in dew collected on surrogate surfaces

Levels of formate and acetate in dew were measured at Dayalbagh, India, using surrogate surfaces. The dew formed per night ranged between 0.06 l m(-2) and 1.38 l m(-2), with an average of 0.59 l m(-2). pH ranged between 6.7 and 7.4. Mean concentrations of formate and acetate in dew were 10.2 +/- 10.2 mu eq l(-1) and 7.5 +/- 4.5 mu eq l(-1), respectively. The correlation coefficient between the two ions was 0.80 (p = 0.001), which suggested that concentrations of these species in dew are linked together. They have either common or different sources with fairly constant strengths or products of same reaction. Good correlation of formate and acetate with Ca (r = 0.82 and r = 0.70, respectively) and Mg (r = 0.74 and r = 0.71, respectively) suggested that these ions may be associated with Ca and Mg after the neutralization process. Deposition rates for formate and acetate in dew per night were 10.2 +/- 7.22 mu mol m(-2) per night and 4.6 +/- 2.2 mu mol m(-2) per night, respectively. The theoretical Henry's law constant (K-H*) and the field-observed Henry's law coefficient (K-H*) as calculated from concurrent measurements of gas phase and dew for both acids showed large discrepancies of three orders of magnitude.