HR: 0800h
AN: A51C-0588    [Abstracts]
TI: Prototype of a Laser-Induced Fluorescence Ground-Based Instrument for Measurements of Atmospheric Iodine Monoxide (IO)
AU: * Co, D T
EM: co@fas.harvard.edu
AF: Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138, United States
AU: Thurlow, M E
EM: thurlow@fas.harvard.edu
AF: Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138, United States
AU: Hanisco, T F
EM: tfh@huarp.harvard.edu
AF: Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138, United States
AU: Lapson, L B
EM: lapson@huarp.harvard.edu
AF: Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138, United States
AU: Anderson, J G
EM: anderson@huarp.harvard.edu
AF: Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, MA 02138, United States
AB: High abundances of iodine monoxide (IO) are known to exist and to participate in local photochemistry of the marine boundary layer: (1) IO participates in depletion episodes of O₃ and in the removal of mercury in the Arctic polar spring by enhancing atomic Br mixing ratios. Recent observations and computer simulations suggest that mercury sequestration is closely tied to halogen photochemistry and that gaseous atomic Hg depletion can be enhanced significantly by the presence of small amounts of iodine-containing compounds. (2) IO and higher- order iodine oxides are involved in the formation of new particles in coastal marine environments. Studies using smog chamber experiments simulating coastal atmospheric conditions have demonstrated that new particles can form from condensable iodine-containing vapors and that their concentrations over the open ocean are sufficient to influence marine particle formation. (3) IO has also been shown to affect the oxidizing capacity of the troposphere by altering the partitioning of NO₂/NO and HO₂/HO and by activating chlorine and bromine in sea salt aerosols. In the stratosphere, these same processes can lead to enhanced ozone loss rates. Detailed photochemical models that include iodine photochemistry, however, are hampered by the lack of observational data. The distribution of IO in vertical, horizontal, and temporal coordinates is unknown, so the impact of IO on global photochemistry cannot be predicted. The resolution of these important scientific issues requires an in situ IO instrument. A fully functional nanosecond Nd:YAG-pumped Ti:Sapphire laser system and a prototype IO ground-based instrument have been built in our lab. With the current setup, the laser system was situated 10 m from the field station, and the laser light was coupled via an optical fiber. With the use of highly efficient fluorescence detection optics and photon counting techniques, sensitivities of better than 0.1 ppt in 1 s for IO was achieved in the laboratory and 1-2 ppt in the field. The design of the instrument and data acquisition system will be described. The prototype was deployed to the Northeastern University Marine Science Center in Nahant, MA in August 2007. Laminaria macroalgae is known to be responsible for coastal I₂ emissions, and Nahant has extensive populations of kelp within the shallow subtidal zone. Results from the field mission will be reported, and future developments of the instrument will be discussed. It is expected that a modified version of this new system will, in time, be capable of being integrated with the existing instrumentation used for the detection of halogen (ClO, BrO), nitrogen (NO₂), and hydrogen (OH and HO₂) free radicals.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0365 Troposphere: composition and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting