Development of a Quantum Cascade Laser-Based Detector for Ammonia and Nitric Acid

65821 Aircraft measurements of ammonia and nitric acid can provide critical information on the sources and sinks of these atmospheric nitrogen species. This is important in understanding air quality, aerosol formation, visibility, and the impact of energy production and usage on global climate change. This project will develop a compact tunable infrared laser differential absorption spectrometer. Based on recent advances in room temperature pulsed quantum cascade lasers, it will greatly improve the sensitivity of real-time airborne measurements for the detection of ammonia and nitric acid at the 10 parts-per-trillion level. In Phase I, detection limits for atmospheric ammonia and nitric oxide, as a surrogate for nitric acid, were demonstrated using Peltier-cooled pulsed quantum cascade lasers at sub-part-per-billion mixing ratios. Measurements of laser line width as a function of electrical pulse shape were combined with a model of thermal heat flow in the laser junction and used to implement an improved pulse driver circuit that will minimize line width and improve detection sensitivity. A siloxyl-coated sampling cell and glass inlet were demonstrated, which minimize surface artifacts when sampling ammonia from the atmosphere. Phase II will design, build, and test a prototype instrument employing multiple quantum cascade lasers for detection of up to four gases simultaneously. Commercial Applications and Other Benefits as described by the awardee: A sensitive, cryogen-free, mid-infrared absorption method for atmospheric trace gas detection should have wide benefits for environmental research, medical diagnostics, and industrial process monitoring of gaseous compounds. Examples include air pollution monitoring, breath analysis, combustion exhaust diagnostics, and plasma diagnostics for semi-conductor fabrication.