Laser-induced-fluorescence-based detection system for measurement of tropospheric OH using 308-nm excitation at low pressure

Andreas Hofzumahaus; Frank Holland

doi:10.1117/12.140228

12 February 1993 Laser-induced fluorescence based detection system for measurement of tropospheric OH using 308 nm excitation at low pressure

Andreas Hofzumahaus, Frank Holland

Author Affiliations +

Proceedings Volume 1715, Optical Methods in Atmospheric Chemistry; (1993) https://doi.org/10.1117/12.140228
Event: Environmental Sensing '92, 1992, Berlin, Germany

Abstract

A detection system for the measurement of tropospheric OH radicals by laser-induced fluorescence has been developed. Ambient air is expanded through a nozzle into a fluorescence cell and is irradiated at low pressure by a pulsed frequency-doubled dye laser. The laser wavelength is tuned to selectively excite the OH radicals on a single rovibronic transition at 308 nm. The OH-resonance fluorescence, emitted mostly between 307 and 311 nm, is detected by a gated photomultiplier/photon counter assembly. This excitation/detection method reduces interferences due to laser generated OH efficiently far below the projected limit of detection. Calibration of our present system yields a detection limit (SNR = 2) of 8.2 x 10 exp 6 OH/cu cm for a 5-min on-resonance and 5-min off-resonance signal integration period at a laser pulse repetition rate of 20 Hz. A considerable improvement of the detection limit to 3.7 x 10 exp 5 OH/cu cm is anticipated by replacing the currently available laser system by a copper-vapor laser pumped dye laser allowing a higher repetition rate of 10 kHz. This would allow useful in situ OH measurements for testing current tropospheric chemistry models.

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Andreas Hofzumahaus and Frank Holland "Laser-induced fluorescence based detection system for measurement of tropospheric OH using 308 nm excitation at low pressure", Proc. SPIE 1715, Optical Methods in Atmospheric Chemistry, (12 February 1993); https://doi.org/10.1117/12.140228

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