Research on vehicle-mounted measurement of NO2 based on cavity ring-down spectroscopy

Abstract

Nitrogen dioxide (NO₂) is a significant atmospheric pollutant with notable impacts on the environment and human health. The measurement of NO₂ concentration is crucial for gas phase analysis in atmospheric chemistry, assessment of regional pollution levels, and improvement of data management systems. In this paper, a highly sensitive cavity ring-down spectroscopy (CRDS) technique has been used to measure the concentration of NO₂. The CRDS system utilizes a diode laser and high reflectivity mirrors (over 99.99 %) at 405 nm, achieving a minimum detection limit of 43 ppt (1σ, 40 s) and 92 ppt (1σ, 10 s) as determined by Allan variance. In order to improve the measurement accuracy and stability, the Kalman filtering has been used to process the background ring-down time and ring-down time, and the minimum detection limit can be increased by about 2.06 times to 45 ppt (1σ, 10 s), while preserving temporal response and reducing noise. Under the condition of atmospheric NO₂ measurement, a comparative experiment was carried out in Hefei with the CEAS system. The linear fitting slope was $1.033\pm 0.017$, and the correlation coefficient reached about 92 %. The CRDS device was integrated for vehicle-mounted measurements of NO₂ concentrations in suburban, urban, and industrial areas of Maanshan City. The experimental result has demonstrated that this system can achieve high-precision, high-sensitivity, and stable measurements of NO₂.