Atmospheric concentrations of carboxylic acids and related compounds at a semiurban site

Atmospheric gas- and particle-phase carboxylic acids and related compounds were measured during October 1991 in a semiurban site in northeastern United States. Formic and acetic acid were present in the atmosphere mostly in the gaseous form with less than 10% in the particle phase. Concentrations of formic acid and acetic acid were in the 0.80–2.5 and 0.60–3.4 ppbv ranges, respectively. Formic acid was correlated with acetic acid (r=0.94). Diurnal variations of formic acid were similar to those of ozone. This pattern is consistent with photochemical production as an important source. Formic-to-acetic acid ratios less than one were recorded, likely due to an increase in acetic acid contribution from direct emissions associated with vehicular traffic. Formaldehyde levels began to decrease after the mid-afternoon maxima; concentrations varied from 0.63 to 3.7 ppbv. Seven carboxylic acids (formic, acetic, pyruvic, glyoxalic, oxalic, succinic, and malonic) in the particle phase were identified. Aerosol carboxylic acid concentrations varied from 26 to 360 ng m−3. About 80% of the carboxylic acid aerosol mass was in the size fraction below 1.0 μm diameter. Of the dicarboxylic acids, oxalic acid was the most abundant species, followed by succinic acid and malonic acid. Particulate total organic carbon exhibited a concentration range of 12.6 × 103−49.9 × 103 ng Cm−3. The observed amounts of carboxylic acids in the particle phase accounted for a small fraction of the organic carbon. Results indicated that photochemical processes and anthropogenic emissions such as automobile exhaust are major sources of atmospheric carboxylic acids.