Volatile inorganic Cl in surface air over eastern North America

Volatile inorganic Cl in surface air over eastern North America was selectively measured using a tandem‐mist‐chamber technique with known collection efficiencies for HCl, HOCl, and Cl 2 . Mixing ratios of total alkaline‐reactive inorganic Cl (Cl t ) and HCl * (including HCl and possibly NOCl, ClNO 2 , and ClNO 3 ) were statistically indistinguishable ranging from <39 to ≈ 2800 pptv; most were <300 pptv. Those of Cl * (including Cl 2 and 56% HOCl) were <26 pptv Cl; anthropogenic influences were undetected. In addition, pre‐ and post‐sunrise concentrations of HCl * were similar suggesting insignificant Cl photochemistry at dawn. HCl appears to be the dominant form of volatile inorganic Cl over eastern North America. Atomic chlorine is probably not an important oxidant in the polluted continental boundary layer.