92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Thursday, 26 January 2012: 8:45 AM
The Development of Quantum Cascade Laser System for Simultaneous Methane-Nitrous Oxide Concentration Retrievals
Room 339 (New Orleans Convention Center )
Paulo Cesar Castillo Sr., The CIty College of New York, New York, NY; and C. Padilla, I. Sydoryk, B. Gross, and F. Moshary

Two major long-lived greenhouse gases in the atmosphere with significant global warming effects are Methane (CH4) and Nitrous-Oxide (N2O). These gases are known to be produced in a number of anthropogenic settings. One such example is manure management systems, which releases substantial GHG's and is mandated by the EPA to provide continuous monitoring Current open path methods for the qualitative and quantitative chemical analysis of trace gases are mainly use of Fourier Transform Spectrometer (FTIR) or near-IR differential optical absorption spectroscopy (DOAS). Although FTIR is suitable for ambient air monitoring measurement of more abundant gases such as CO2 and H20 etc., the lack of spectral resolution makes the retrieval of weaker absorbing features such as N20 more difficult for FTIR. The use of tunable portable high spectral resolution Quantum Cascade Laser (QCL) sources offers an attractive alternative. This presentation will provide the modeling and system development status on our efforts to develop a novel field deployable open path system using a chirped single distributed-feedback QCL, operated at 7.78um with an optimal spectral window of 1297.5 1299.5 cm-1 with .01 cm-1 resolution, to retrieve simultaneous ambient concentrations of methane/nitrous-oxide. The system layout is shown in the Figure 1. To assess theoretical feasibility, the required SNR based on the spectral modeling of all atmospheric trace gases including interfering species was conducted was calculated to achieve ambient retrievals at 1% accuracy. For path lengths of 100m, the required SNR was estimated ~ 400. These SNR constraints were then used with a per-pulse SNR obtained from a link power budget analysis accounting for the transmitter, receiver and link parameters, to demonstrate feasibility of a real-world system. In addition, we will present laboratory gas-cell tests for ambient STP conditions for H20 and CH4, N20 using different temperature tunings and compare against existing measurements from FTIR and analytical point sensors. Figure1. The Open-path Ambient Gas Monitoring Mono-static System

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