9360606 Nelson The possibility that atomic chlorine concentrations in the marine surface layer are large enough to compete with the hydroxyl radical as the major tropospheric oxidizer has received considerable speculation. Chlorine atoms participate in the oxidation of hydrocarbons and dimethyl sulfide and can also directly influence tropospheric ozone loss through catalytic cycles with chlorine monoxide and the hydroperoxy radicals. The net effect on the ozone budget may be highly dependent on the partitioning of the inorganic chlorine pool between hydrochloric acid, hypochlorous acid, chlorine gas, and chlorine nitrate. In order to assess the potential importance of chlorine chemistry, direct measurements of these species are necessary. In Phase I of this research, the PIs will assess the feasibility of detecting hypochlorous acid at the 10 to 20 ppt level using tunable diode laser infrared absorption. This will require (1) measurement of pressure broadening coefficients for selected absorption lines, (2) identification of suitable spectral regions, (3) investigation of photolytic modulation of hypocholorous acid to implement background subtraction, and (4) design of novel multiple pass absorption cell with a path length of at least 600 meters. Phase II research will improve the basic spectroscopic parameters for quantifying hypochlorous acid concentrations and develop a prototype field instrument capable of simultaneous measurements of hydrochloric acid and hypochlorous acid in the marine atmosphere. ***
