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Open-path Detection of Atmospheric Nitrogen Species

Speaker: Kang Sun, Graduate Student
Series: EEWR Brown Bag Seminars
Location: Engineering Quad E219
Date/Time: Friday, March 25, 2011, 12:00 p.m. - 1:00 p.m.

Abstract:

Nitrous oxide (N2O) and Ammonia (NH3) are the second and third most abundant nitrogen species in the atmosphere. They play key role in global geochemical cycle, climate change, stratospheric ozone depletion, and aerosol particle pollution. We develop compact, fast, and low power sensors for detection of atmospheric N2O and NH3. The technique is based on atmospheric absorption of these trace species in the mid-infrared region, using a quantum cascade (QC) laser source. The open-path design simplifies the sampling process and enhances the portability for extended period of unattended operation of the sensor. Both sensors are developed and calibrated independently in the laboratory, and deployed in field for air quality measurements.

In the presentation I will discuss open-path NH3detection and its calibration involving a novel technique which utilizes ethylene (C2H4) as a reference gas. The absorption lineshapeparameters of NH3and C2H4were characterized and theoretically modeled in order to quantify the precision of the method. Results show that C2H4can serve as a proxy gas for NH3with an accuracy of about 10%. The presentation will also discuss the optimization of sensor optical components. The reflective/transmissivesurfaces cause optical interferences that are identified by evaluating the Fourier transform of the detector signal. Finally, I will discuss the design and performance of N2O/CO sensor. We show that for the first time CO (which is a tracer for N2O emissions) and N2O are detected simultaneously at a 2 second measurement. In addition, the sensor is also capable of measuring H2O by appropriate current tuning the laser scan. H2O measurements are useful in calculating the dry mixing ratio of N2O/CO. Preliminary results of field deployment of the sensor for atmospheric measurements will be presented.