Highly precise measurement of atmospheric N2O and CO using improved White cell and RF current perturbation

Abstract

A highly precise dual gas sensor for measurement of atmospheric nitrous oxide (N2O) and carbon monoxide (CO) was developed and evaluated. A room temperature interband cascade laser emitting at 4.54 μm was used as a laser source to cover the absorption lines of N2O and CO simultaneously. Sensitivity and precision were enhanced by using an improved White cell with 76 m effective optical path length and radio frequency noise perturbation technique to reduce optical interference noise. A method was proposed to correct the laser frequency by calculating the correlation coefficient between the absorption signal with the reference signal, which effectively reduced the long-term drift of the absorption line center to less than 4 × 10−5 cm−1. By further precisely control the temperature and pressure of the absorption cell, a continuous 24 h measurement precision of 65 ppt N2O and 133 ppt CO at 0.1 Hz was demonstrated, with a daily drift less than 1.5 ppt. Finally, the repeatability and reliability of the sensor system were validated by real atmospheric measurements for two consecutive days.