Grantee Research Project Results
2002 Progress Report: Development of All-Solid-State Sensors for Measurement of Nitric Oxide and Carbon Monoxide Concentrations by Optical Absorption
EPA Grant Number: R828180Title: Development of All-Solid-State Sensors for Measurement of Nitric Oxide and Carbon Monoxide Concentrations by Optical Absorption
Investigators: Walther, Thomas , Caton, Jerry , Lucht, Robert P.
Institution: Texas A & M University
EPA Project Officer: Hahn, Intaek
Project Period: July 1, 2000 through June 30, 2002
Project Period Covered by this Report: July 1, 2002 through June 30, 2003
Project Amount: $225,000
RFA: Exploratory Research - Engineering, Chemistry, and Physics) (1999) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Water , Land and Waste Management , Air , Safer Chemicals
Objective:
The overall objective of this research project is the development of new optical sensors for the detection of nitric oxide (NO) and carbon monoxide (CO) in the exhaust streams of combustion systems. Sensors based on absorption measurements combine high sensitivity and real-time capabilities. Present sensors rely on physical sampling techniques, which are inherently slow.
The specific objectives of this research project are to: (1) develop a diode-laser-based UV absorption sensor for NO measurements and a diode-laser-based mid-infrared absorption sensor for CO measurements; (2) characterize the performance of the sensors by absorption measurements in a gas cell, simulated combustion exhaust streams, and well-characterized flames, and by comparison with Fourier transform infrared (FTIR) measurements and/or probe sampling; and (3) complete a feasibility study on the incorporation of the sensor systems in practical systems for pollutant monitoring and control.
Progress Summary:
During the last year, we have successfully developed both the NO sensor and the CO sensor, and tested these sensors in both gas cells and in the exhaust of an operating gas turbine engine at Honeywell Corporation in Phoenix, AZ.
An all-solid-state continuous-wave (CW) laser system for ultraviolet absorption measurements of the NO molecule was developed and demonstrated. The single-mode, tunable output of a 10-mW, 395-nm external-cavity diode laser (ECDL) is sum-frequency-mixed with the output of a 115-mW, frequency-doubled, diode-pumped CW Nd:YAG laser in a beta-barium borate crystal to produce approximately 50 nW of tunable CW radiation at 226.7 nm. The wavelength of the 395-nm ECDL is then scanned so that the wavelength of the ultraviolet beam is tuned over NO absorption lines to produce a fully resolved absorption spectrum. Ultraviolet laser radiation is detected using a solar-blind photomultiplier tube. The estimated NO detection limit of the system for a demonstrated absorption sensitivity of 2 x 10-3 is 0.2 ppm per meter of path length for 300 K gas. Measurements were performed in a gas cell using calibrated mixture of NO in N2 buffer gas, and the concentrations obtained from the absorption measurements are consistent with the calibrated concentrations.
The diode-laser-based CO sensor layout is based on difference-frequency-mixing in a periodically poled lithium niobate (PPLN) crystal to obtain approximately 1 µW of narrowband, CW laser radiation at 4.5 µm. The fundamental beams for this non-linear process are 1,064 nm and 861 nm. The 1,064-nm laser is a Nd:YAG system that provides 550 mW of 1,064.664 nm radiation. The 861-mn laser is an 80-mW tunable ECDL system that can be tuned mode-hop free over a 10 GHz range. The ECDL radiation is tuned so that the generated infrared is tuned over the R-branch transitions of the CO molecule. Once the mid-infrared laser radiation is generated infrared, the beam is split into a reference beam, a second beam that is sent through the gas cell or through exhaust gases. Both beams are detected using InSb detectors.
Both of these sensors were used for measurements in the exhaust stream of an operating auxiliary power unit (APU) gas turbine engine in a series of tests at Honeywell in Phoenix, AZ, during July. During these tests NO was measured in the exhaust at levels below 10 ppm. For measurements at levels above 20 ppm, the NO emission levels obtained using our new ultraviolet absorption sensor corresponded with the results of probe sampling chemiluminescent analyzer results to within 1-2 ppm. The results of the CO mid-infrared absorption measurements are still being analyzed, but concentrations obtained from our absorption measurements appear to be nearly a factor of 2, low compared to probe sampling measurements. We currently are investigating our CO spectral model and potential CO2 interferences in gas cell measurements in an attempt to understand the source of this discrepancy.
Future Activities:
During the remaining time period for the EPA grant, we will concentrate on the following activities: (1) improvement and testing of the CO spectral code, performing more gas cell measurements; (2) extension of the wavelength of the CO sensor into the range between 4.5 and 5.0 µm, and investigation of the multi-pass potential of the NO absorption sensor; and (3) investigation of wavelength modulation spectroscopy for increasing the sensitivity of the NO measurements.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 13 publications | 2 publications in selected types | All 2 journal articles |
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Type | Citation | ||
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Hanna SF, Barron-Jimenez R, Anderson TN, Lucht RP, Caton JA, Walther T. Diode-laser-based ultraviolet absorption sensor for nitric oxide. Applied Physics B-Lasers and Optics 2002;75(1):113-117. |
R828180 (2002) R828180 (Final) |
not available |
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Ray GJ, Anderson TN, Caton JA, Lucht RP, Walther T. OH sensor based on ultraviolet, continuous-wave absorption spectroscopy utilizing a frequency-quadrupled, fiber-amplified external-cavity diode laser. Optics Letters 2001;26(23):1870-1872. |
R828180 (2000) R828180 (2002) R828180 (Final) |
not available |
Supplemental Keywords:
pollutant monitor, pollutant emissions, diode lasers, optical sensors, nitric oxide, carbon monoxide, fiber amplifiers, RFA, Scientific Discipline, Air, Toxics, Waste, Environmental Chemistry, Physics, HAPS, Environmental Monitoring, tropospheric ozone, Engineering, Chemistry, & Physics, EPCRA, Incineration/Combustion, Fourier Transform Infrared measurement, air quality standards, fiber ampiliers, risk assessment, nitrous oxide, combustion systems, pollutant monitoring, probe sampling, carbon monoxide (CO), air sampling, ambient emissions, chemical detection techniques, smog, carbon monoxide, laser based optical sensor, Nitric oxide, nitric oxide (NO), combustion, diode laser, diode laser spectrometer, optical absorptionRelevant Websites:
http://faculty.physics.tamu.edu/walther Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.