Evidence of inorganic chlorine gases other than hydrogen chloride in marine surface air

Abstract

We report the first measurements of inorganic chlorine gases in the marine atmosphere using a new tandem mist chamber method. Surface air was sampled during four days including one diel cycle in January, 1992, at Virginia Key, Florida. Concentrations of HCl* (including HCl, ClNO 3 , ClNO 2 , and NOCl) were in the range 40 to 268 pptv and concentrations of Cl 2 * (including Cl 2 and any HOCl not trapped in the acidic mist chamber) were in the range <26 to 254 pptv Cl. Concentrations of Cl 2 * increased during the night, and decreased after sunrise as HCl* concentrations increased by similar amounts. The measurements suggest an unknown source of either HOCl or Cl 2 to the marine atmosphere. Photochemical model calculations indicate that photolysis of the observed Cl 2 * would yield a chlorine atom (Cl•) concentration of order 10 4 –10 5 cm −3 . Oxidation by Cl• would then represent a significant sink for alkanes and dimethylsulfide (DMS) in the marine boundary layer. The cycling of Cl• could provide either a source or a sink for O 3 , depending on NO X levels.