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, ClNO3, ClNO2, and NOCl) were in the range 40 to 268 pptv and concentrations of Cl2* (including Cl2 and any HOCl not trapped in the acidic mist chamber) were in the range <26 to 254 pptv Cl. Concentrations of Cl2* 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 Cl2 to the marine atmosphere. Photochemical model calculations indicate that photolysis of the observed Cl2* would yield a chlorine atom (Cl•) concentration of order 104–105 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 O3, depending on NOX levels.
Highlights
There has been recurring speculationover the yearsas to the possiblerole of atomicchlorine(C1.) in the chemistry of the marine boundarylayer [Wofsyand McElroy, 1974; Finlayson-Pitts, 1983; Finlayson-Pittset al., 1989; Keeneet al., 1990]
Singhand Kasting[1988] reviewed the availabledata on sourcesof CIofrom (1) oxidationof HC1andCH3C1,(2) photolysisof chlorocarbons(,3) aerosol reactionsof C1NO3, and (4) reactionsof nitrogen oxides on dry NaC1 aerosol
The observedconcentrationosf HNO3, SO2 (Table 1) and total aerosolNO3, non-sea-salt SO4=, NH4*, and black carbon(Table 2) suggesthat the air sampledwas relativelyunpollutedfor the locale,but certainlypolluted compared to subtropical North Atlantic background
Summary
There has been recurring speculationover the yearsas to the possiblerole of atomicchlorine(C1.) in the chemistry of the marine boundarylayer [Wofsyand McElroy, 1974; Finlayson-Pitts, 1983; Finlayson-Pittset al., 1989; Keeneet al., 1990]. Singhand Kasting[1988] reviewed the availabledata on sourcesof CIofrom (1) oxidationof HC1andCH3C1,(2) photolysisof chlorocarbons(,3) aerosol reactionsof C1NO3, and (4) reactionsof nitrogen oxides on dry NaC1 aerosol. They concludedthat these processesare too slow to have much effect on the chemistry of the marine boundary layer, recent work [e.g.,Ganskeet al., 1992]suggesttshatreactionsinvolving nitrogenoxidesmay be more importantthan estimatedby Singhand Kasting [1988]. A fraction of HOC1 may have been trapped in the acidic mist chamber. Standard additions to mist chamber solutions indicate, ,that HOC1 doesnot generateC1-and is thusnot detectedby the ion chromatographicanalyticaltechnique. We use the symbolC12' to denotethis chlorine. It doesnot appearthat organicchlorinegasesare collectedin eithermist chamber[Keeneet al., 1993]
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