9423289 Nelson The possibility that atomic chlorine concentrations in the marine surface layer are large enough to compete with hydroxyl radical (OH) as the major tropospheric oxidizer continues to receive considerable speculation. Chlorine atoms participate in the oxidation of hydrocarbons, dimethyl sulfide, and can also directly influence tropospheric ozone loss through catalytic cycles with chlorine monoxide (ClO) and hydroperoxy (HO2) radicals. The net effect on the ozone budget may be highly dependent on the partitioning of the inorganic chlorine pool between four chlorine-containing gases; hydrogen chloride (HCl), hypochlorous acid (HOCl), molecular chlorine (Cl2), and chlorine nitrate (ClONO2). To assess the potential importance of chlorine chemistry in the lower atmosphere, direct measurements of these species are necessary. In Phase I of this research, the feasibility of detecting both HCl and HOCl down to the 10 to 20 part-per-trillion (pptv) concentration range by tunable diode infrared laser absorption was demonstrated. The Phase II research effort will improve the basic spectroscopic parameters for quantifying HOCl concentrations in the atmosphere, and develop and construct a prototype field instrument capable of simultaneous measurements of HCl and HOCl in the marine troposphere. This new instrument will be laboratory tested and evaluated against existing, albeit nonselective, inorganic chlorine techniques in an intercomparison. The instrumentation produced as a result of this research program will be useful for measuring other trace gases in addition to HCl and HOCl. The novel long path, multiple pass absorption cell developed during this project will have independent commercialization potential for other laser absorption systems used to monitor industrial pollutants, toxic wastes, and various gases emitted from combustion processes.
