Development of a Laser-Induced Fluorescence Ground-Based Instrument for Measurements of Atmospheric Iodine Monoxide (IO)
Abstract
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 sensor. A fully functional nanosecond Nd:YAG-pumped Ti:Sapphire system and an IO sensor have been built in our lab. With the use of highly efficient fluorescence detection optics and photon counting techniques, a sensitivity of better than 0.1 ppt in 1 s for IO was empirically determined with our current laboratory prototype system, sensitive enough to resolve both the dilute mixing ratios of tropospheric and stratospheric IO and fast enough to resolve its highly inhomogeneous abundance in the marine boundary layer. Calibration of the instrument was achieved via two independent techniques: (1) The application of cavity ringdown spectroscopy and (2) the generation of known concentrations of IO via standard addition. This new instrument will be deployable in both ground-based and airborne campaigns to address the different facets of iodine photochemistry in the atmosphere. It is expected that a modified version of this new system will, in time, be integrated with the existing instrumentation used for the detection of halogen (ClO, BrO), nitrogen (NO2), and hydrogen (OH and HO2) free radicals.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.A53B0192C
- Keywords:
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- 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0305 Aerosols and particles (0345;
- 4801;
- 4906);
- 0315 Biosphere/atmosphere interactions (0426;
- 1610);
- 0365 Troposphere: composition and chemistry;
- 0394 Instruments and techniques