A novel calibration method for atmospheric NO3 radical via high reflectivity cavity

The NO3 radical is one of the important indicators of atmospheric oxidation capability at night, and its accurate detection has been extensively investigated. High reflectivity cavity instruments, such as cavity ring-down spectroscopy (CRDS) and cavity-enhanced absorption spectroscopy (CEAS), are generally employed for NO3 radical detection. However, sampling detection easily adsorbs radicals on surfaces, which causes complications and even additional loss. According to the chemical conversion relationship between NO3 radical and NO2, a method of absolute calibration different from the previous relative calibration method is applied by combining the CRDS and CEAS instruments for the NO3 radical and NO2, respectively. Experimental results show that the overall transmission efficiency of the NO3 radical for the CRDS instrument is approximately 75% +/- 9% at a flow rate of 6.5 SLPM. Comparative experiments between the two methods are conducted to estimate the accuracy of this method. The achieved results indicate that absolute calibration is a reliable and feasible method for radical calibration in the laboratory. Furthermore, the absolute calibration method has the potential to realize accurate real-time calibration in field measurements.