Department of Earth System Science

Measurements of Cl₂ in coastal urban air were made in Irvine, California from Aug.-Nov., 2005, using negative ion atmospheric pressure chemical ionization with tandem mass spectrometry. Cl₂ ranged from <2.5 to 20 ppt with a two month mean of 3.5 ± 3.5 ppt (1σ) and an average noon photolysis rate of 44 ppt hr⁻¹ Cl₂. Model calculations suggest that Cl₂ photochemistry results in an increase of 5–8 ppb in daily maximum O₃ levels, relative to a base case scenario without Cl₂.