Gas Phase C2−C10 Organic Acids Concentrations in the Los Angeles Atmosphere

The atmospheric concentrations of gas-phase C2−C10 monocarboxylic and benzoic acids are reported in samples collected during a severe Los Angeles area photochemical smog episode. Average urban concentrations are 10−50 × greater than concentrations observed at a remote background location, indicating an anthropogenic origin for these compounds. Average urban concentrations during the episode were 16.1 μg m-3 (6.6 ppb) for acetic acid and 1.67 μg m-3 (0.55 ppb) for propionic acid, with progressively lesser amounts as the carbon chain length of the acids is increased. Spatial and diurnal variations in atmospheric organic acids concentrations point to the importance of both direct emissions from primary sources and formation by photochemical reaction of precursor compounds.