Development of Diode-Laser-Based Laser-Induced Fluorescence for in Situ Atmospheric Detection of NO and SO2

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9522028 Wofsy This project will focus on the development and optimization of a diode-laser-based, laser-induced fluorescence (LIF) system for in situ detection and quantification of sulfur dioxide (SO2) in the troposphere and stratosphere. The research plan will exploit very recent advances in diode lasers and associated optical technologies in an effort to construct an instrument that is significantly smaller, lighter, more efficient (lower power consumption), less expensive, and more sensitive. In situ measurements of SO2 at ultra-trace concentrations are required to address several prominent issues in atmospheric chemistry. Sulfur-containing gases play important roles in the chemistry of the global troposphere, in local and regional pollution, in the biogeochemical sulfur cycle, and in the formation of sulfate aerosols in both the troposphere and stratosphere. The primary anthropogenic sulfur gas is SO2, but no high-sensitivity, fast response instrument exists for in situ detection of SO2 at the low parts-per-trillion (pptv) concentration range. The detection scheme that will be investigated during this project has a proposed detection limit of 2 pptv/sec for sulfur dioxide and a size compatible with airborne deployment platforms. Collaborative investigations between researchers at Harvard University and the Naval Research Laboratory have recently demonstrated the ability to generate the tunable 215-220 nm UV radiation required for SO2 LIF by frequency quadrupling a diode laser. Further development, optimization, and testing of the performance features of this diode-laser-based UV source will be performed during the course of this grant. The minimum goals of this continuing research effort will be to attain an average laser power of at least 100 uW at 220 nm, while maintaining a sufficiently narrow linewidth of 0.10 cm-1. Consideration for future funding will be contingent on successful demonstration of these minimum performance specifications. If successful, the generali ty of fluorescence detection and the relatively wide tunability of the proposed diode laser system will permit applications to a number of other molecules (for example, nitric oxide) and environments.