ANYL 187 |
| Cavity-enhanced spectroscopy methods provide a powerful tool for quantifying ultra-trace levels of reactive radicals in the atmosphere and measuring their reactivity in the laboratory. We have exploited off-axis cavity-ring down spectroscopy to measure the nitrate radical, NO3, and dinitrogen pentoxide, N2O5 in the ambient atmosphere and in the laboratory. These compounds are intermediates in the nighttime oxidation of nitrogen dioxide and nitric oxide, NOx, and provide key insight into the mechanism of nocturnal NOx oxidation. We have built a field instrument to detect NO3 + N2O5 based upon a small, cheap, portable diode laser and a highly reflective optical cell. Our system uses an off-axis geometry to simplify the alignment and provide immunity against vibrations. The system acheives a high repetition rate (~500 Hz) that is only limited by the long ring-down time of the system (~160 microseconds). The detection limit is approximately one part per trillion (1 part in 1012) by volume in one second integration time. Detection of these intermediates and quantification of their concentrations and loss rates in the Arctic wintertime atmosphere provides a picture of atmospheric chemistry that would have been unavailable without cavity enhanced spectroscopy. This application of cavity enhanced spectroscopy shows that the technique is ready to advance the field of environmental spectroscopy. |
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Has Cavity-Enhanced Detection Come of Age?
8:30 AM-11:30 AM, Monday, 11 September 2006 Moscone Center -- Room 130, Oral
Division of Analytical Chemistry |