Measurement of Cl2 in coastal urban air

Measurements of Cl-2 in coastal urban air were made in Irvine, California from Aug.-Nov., 2005, using negative ion atmospheric pressure chemical ionization with tandem mass spectrometry. Cl-2 ranged from < 2.5 to 20 ppt with a two month mean of 3.5 +/- 3.5 ppt (1 sigma) and an average noon photolysis rate of 44 ppt hr(-1) Cl-2. Model calculations suggest that Cl-2 photochemistry results in an increase of 5-8 ppb in daily maximum O-3 levels, relative to a base case scenario without Cl-2.