Zusammenfassung
This work gives a detailed characterization of a laboratory setup for photoacoustic NO2 trace gas detection at the ppb level. The signal generation is based on the excitation of electronic B-2(2) and B-2(1) states using a low-cost semiconductor laser emitting at 450 nm. An acoustic resonator was used for signal amplification and the modulation frequency of the laser was determined to 3395 Hz in ...
Zusammenfassung
This work gives a detailed characterization of a laboratory setup for photoacoustic NO2 trace gas detection at the ppb level. The signal generation is based on the excitation of electronic B-2(2) and B-2(1) states using a low-cost semiconductor laser emitting at 450 nm. An acoustic resonator was used for signal amplification and the modulation frequency of the laser was determined to 3395 Hz in order to gain maximum signal amplification. The quality of resonant amplification was determined to 7.9. The gas samples were NO2 calibration gases diluted with pure nitrogen. The signal-to-noise ratio (SNR) dependency on the flow rate Q and the lock-in time constant tau(LlA) was investigated, respectively, and the optimum values were specified to Q=500 mL/min and tau(LlA) = 2s. In case of ambient noise, increasing tau(LlA) to 10 s was evaluated as sufficient for SNR preservation. The noise level was measured in the absence of NO2 and it was determined to be composed of 51% electronic noise and 49% gas flow noise. With the analyte concentration ranging from 300 ppbV to 100 ppmV, the linear dependency of the photoacoustic amplitude on the NO2 concentration was specified, the sensitivity was determined to 110 mu V/ppmV and the maximum measurement error was calculated to +/- 0.8%. The detection limit was determined to 2.0 ppbV. Furthermore, the stability of the signal was investigated and a maximum drift of +/- 1% was observed within a measuring period of 30 min. The response time tau(90) was specified to 58s. All results considered, this photoacoustic measuring system, which is based on low-cost signal generation and detection units, provides an excellent basis in view of developing a portable device for photoacoustic trace gas detection. (C) 2017 Elsevier B.V. All rights reserved.
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