High-Precision Photoacoustic Nitrogen Dioxide Gas Analyzer for Fast Dynamic Measurement

Abstract

A high-precision photoacoustic (PA) gas analyzer for fast dynamic measurement of ambient nitrogen dioxide (NO2) was developed. The PA analyzer used a differential PA cell combined with two mufflers to achieve rapid gas flow gas detection. A high-power laser diode (LD) with a center wavelength of 450 nm was used as the PA signal excitation source. To reduce the saturated absorption effect of NO2, ambient air was pumped into the analyzer at a flow rate of 900 sccm. Two mufflers were combined with the differential PA cell to reduce the noise caused by the airflow and pump. The parameters of the mufflers were optimized by using a finite element method. The experimental results showed that the gas flow noise was suppressed by 95%. The response time of the PAS analyzer was 34 s. The detection limits of the analyzer were 0.64 and 0.17 ppb when the integration times were 1 and 15 s, respectively. A 120 h continuous monitoring result was compared with the data from the National Environmental Monitoring Station to demonstrate the high reliability of the analyzer.

High-Precision Multipass Fiber-Optic Photoacoustic Gas Analyzer Based on 2f/1f Wavelength Modulation Spectroscopy

“…Photoacoustic (PA) spectroscopy (PAS) is one of the key sensitive gas analysis technologies. − Compared with direct absorption spectroscopy, − it has the characteristics of no background, which is beneficial to improve the sensitivity of gas detection. , Among various PAS systems, − the fiber-optic PA sensor uses a fiber interferometers to detect PA signals, which has the advantage of intrinsic safety. − The fiber-optic PA sensor based on the extrinsic Fabry–Perot (F–P) interference (EFPI) has the characteristic of a simple structure andrealizes the high-sensitive detection of the PA signal. − However, when the fiber-optic PA sensor is installed into the traditional resonant PA cell, the volume of the gas chamber is very large. According to the basic principle of PA gas detection, the PA signal is enhanced with a decrease in the volume of the gas chamber.…”

Differential Cantilever Enhanced Fiber-Optic Photoacoustic Sensor for Diffusion Gas Detection

“…Photoacoustic (PA) spectroscopy (PAS) based gas detection technology has played a critical role in industrial fields. − Compared with other spectral detection technologies, such as tunable diode laser absorption spectroscopy, Raman spectroscopy, PAS has the peculiarities of background free, high sensitivity, and compact size. − The principle of the PAS gas detection is that target gas selectively absorbs light energy, causing the surrounding gas to expand and contract periodically, which is manifested in the form of PA pressure waves. − Consequently, the sensitivity of the acoustically sensitive components is the core factor that determines the detection index of sensing systems. By selecting high-sensitivity acoustic wave sensitive components, the detection indicators of the PA gas sensor can be effectively improved. − However, the higher sensitivity of the system is also accompanied by a decrease in the stability.…”

Rapid Photoacoustic Exhaust Gas Analyzer for Simultaneous Measurement of Nitrogen Dioxide and Sulfur Dioxide

“…Photoacoustic (PA) spectroscopy (PAS) is one of the most promising trace gas detection methods. − Compared with the normal detection methods, PAS has the advantage of fast response, low interference, high sensitivity, and portability. − At present, many PAS systems have been proposed for the detection of SO 2 and NO 2 . The usual exciting sources of PA signal are quantum cascade laser (QCL), − distributed feedback (DFB) laser, − light-emitting diode (LED), , laser diode (LD) − and infrared thermal radiation source. − For SO 2 detection, QCL can operate at the fundamental absorption bands of the SO 2 molecule. Because of the strong absorption of the molecules and the high power of QCL, a brilliant minimum detection limit can be achieved .…”