Cavity Attenuation Phase Shift Spectroscopic Detection of Nitrogen Dioxide

72080-Nitrogen dioxide emissions are regulated by a national ambient air quality standard under the 1970 Clean Air Act. The prevalent means of detection, a chemiluminescence-based monitor (the so-called NOx box), often provides inaccurate readings for nitrogen dioxide in the presence of other nitrogen-containing trace atmospheric species. This project will build an uncomplicated, inexpensive, and accurate spectroscopic sensor for the detection of nitrogen dioxide at the sub-part-per-billion level using Cavity Attenuation Phase Shift spectroscopy (CAPS), a technique related to cavity ringdown laser absorption spectroscopy. It relies on the measurement of small shifts in the phase of modulated light that is transmitted through a resonant optical cavity induced by the absorption of the target species. In Phase I, a proof-of-principle demonstration of a CAPS-based nitrogen dioxide sensor was performed. Results indicated that the CAPS-based sensor had sensitivity less than 1 part per billion of nitrogen dioxide. A calibrated CAPS sensor accurately monitored ambient NO2 concentrations at the 0-40 ppb level over the course of a two day observation period, without the need for human intervention. In Phase II, an improved field-hardened prototype instrument, intended to provide sensitivity less than 1 ppb of NO2 with a 30 second sampling time, will be designed, built, and tested. Commercial Applications and Other Benefits as described by awardee: Compact, inexpensive and accurate nitrogen dioxide point sensors, suitable as tools for the measurement of urban pollution, will be needed as concerns about atmospheric pollution increase. Markets for this instrument should include the atmospheric research community, and entities that provide routine monitoring of exhaust from gas turbines, chemical plants, and refineries.