Development of a 443 nm diode laser-based differential photoacoustic spectrometer for simultaneous measurements of aerosol absorption and NO2

Abstract

Measurement of ambient aerosol and nitrogen dioxide (NO 2 ) is important as they are major pollutants from the burning of fossil fuel and biomass. In the present work, a differential photoacoustic spectrometer (D-PAS) was developed for simultaneous, online measurements of aerosol optical absorption and NO 2 concentration. A novel photoacoustic resonator was designed and employed in the D-PAS for controlling a large flow rate, improving response time, and keeping the flow noise at a low level. The detection limits of 1.0 Mm −1 and 0.87 ppb for aerosol absorption and NO 2 concentration measurements were achieved with a lock-in amplifier time constant of 1 s. The D-PAS accuracy was demonstrated by performing a long-time, continuous measurement of aerosol, and NO 2 in ambient air. The measured results of NO 2 are consistent with the NOx analyzer and environmental monitoring station results.

Quartz-enhanced photoacoustic NH3 sensor exploiting a large-prong-spacing quartz tuning fork and an optical fiber amplifier for biomedical applications

“…Quartz-enhanced photoacoustic spectroscopy (QEPAS), an improved version of traditional PAS, employs a small-size, high-Q-factor quartz tuning fork (QTF) instead of a conventional microphone as a resonant acoustic transducer. The key innovation of QEPAS is the use of the QTF with high resonance frequency (up to several kHz) and narrow frequency band (few Hz or less), which results in an improved immunity of the QEPAS system to ambient noise [18] , [19] , [20] , [21] , [22] , [23] , [24] , [25] , [26] , [27] , [28] , [29] , [30] , [31] , [32] , [33] , [34] , [35] , [36] , [37] , [38] , [39] , [40] , [41] , [42] , [43] , [44] , [45] , [46] , [47] , [48] , [49] . Moreover, QEPAS has a simple spectrophone design and is capable to analyze trace-gas samples of few mm 3 in volume, providing a high detection sensitivity level and fast response time, and hence is very suitable for detecting exhaled gas in real time, as demonstrated in [35] , [36] .…”

Sensitivity enhanced NIR photoacoustic CO detection with SF6 promoting vibrational to translational relaxation process

“…Many researchers have verified that the modulation frequency has significantly impacts on the performance of PAS-based sensor [29] , [38] . Hence, it will be optimized to obtain high-sensitive CO detection in the following experiments.…”

“…For traditional PAS sensor, the acoustic signal is converted to electric signal by a sensitive microphone. The obtained electric signal U PA at the weak absorption regime can be expressed as [28] , [29] : where S O is the microphone sensitivity (unit: mV/Pa), P (λ) is the excited light power at the chosen absorption line, C C ell is the photoacoustic cell constant which generally relates to the PAC geometry, modulation frequency of light and physical characteristic of carrier gas, α (λ) represents the gas absorption coefficient. Obviously, the U PA is directly proportional to absorption coefficient α (λ) at the weak absorption regime when other parameter remains unchanged.…”

Experimental Research on Measuring the Concentration of CO2 in Gas-Liquid Solution Based on PZT Piezoelectric-Photoacoustic Spectroscopy

“…The collection of the photoacoustic signal is accomplished by the PZT piezoelectric ceramic microphone and plays an essential role in the measurement of CO 2 concentration. In addition, the size of the photoacoustic cell has a direct impact on the resonant frequency of the photoacoustic cell, the intensity of the photoacoustic signal generated by the analyte in the photoacoustic cell, and the sensitivity of the measuring device [3,27].…”