Gas phase C-2-C-10 organic acids concentrations in the Los Angeles atmosphere

The atmospheric concentrations of gas-phase C-2-C-10 monocarboxylic and ben zoic acids are reported in samples collected during a severe Los Angeles ar ea photochemical smog episode. Average urban concentrations are 10-50 x gre ater than concentrations observed at a remote background location, indicati ng an anthropogenic origin for these compounds. Average urban concentration s during the episode were 16.1 mu g m(-3) (6.6 ppb) for acetic acid and 1.6 7 mu g m(-3) (0.55 ppb) for propionic acid, with progressively lesser amoun ts as the carbon chain length of the acids is increased. Spatial and diurna l variations in atmospheric organic acids concentrations point to the impor tance of both direct emissions from primary sources and formation by photoc hemical reaction of precursor compounds.