A research team led by Prof. ZHANG Weijun at the Hefei Institutes of Physical Science of the Chinese Academy of Sciences has developed a new detection technology that enables rapid and sensitive detection of nitrogen dioxide (NO₂). Relevant results were published in Analytical Chemistry.

NO₂ is a major pollutant affecting air quality, highly sensitive and accurate measurement of NO₂ is of great significance to atmospheric chemistry research and air pollution prevention and control.  

In this research, the researchers applied amplitude modulation technique to a multimode diode laser for the first time, and developed an amplitude modulated multimode-diode-laser-based Cavity Enhanced Absorption Spectroscopy (AM-CEAS) system for extremely sensitive NO₂ detection.

The new instrument uses phase-sensitive detection for ultra-sensitive absorption measurement. The accuracy of the it is over four times lower than that of the Cavity Ring-down Spectroscopy (CRDS) method using the same instrument during one second and 30 seconds of data acquisition time.  

Combined with ring-down time measurement, the AM-CEAS method eliminates the calibration process of mirror reflectivity and achieves the measurement of absolute concentration of NO₂. It also has the advantages of high injection efficiency, low cavity-mode noise and phase-sensitive detection of modulation spectroscopy.  

The AM-CEAS instrument is a simple, reliable, low-cost, self-calibration tool suitable for long-term stability and low maintenance requirements, with good prospects for scientific research and business applications.  

Currently, the newly developed instrument is being used for comprehensive field observation in Beijing to measure total reactive nitrogen in the atmosphere during the Beijing 2022 Winter Olympics.  

This research was supported by the National Natural Science Foundation of China, the Second Tibetan Plateau Scientific Expedition and Research program, and the Youth Innovation Promotion Association of CAS, etc.

Schematic diagram of the experimental setup of the AM-CEAS instrument. (Image by ZHOU Jiacheng) 

Performance evaluation of the AM-CEAS method and comparison with CRDS measurements. (Image by ZHOU Jiacheng)