Comparisons of CEAS, PC-CLD, and CRDS for NO₂ measurements under a complex atmosphere in Chengdu, China

Nitrogen dioxide (NO₂) plays an important role in atmospheric chemistry. NO₂ detection systems with high precision and low interference have gradually developed into an essential components of measurement instruments for peroxy radical, organic nitrates, and the ozone production rate. Accurate and quantitative evaluations of measurement interference are necessary for field applications. Long-term, multi-scale field comparison experiments were conducted in summer (from August 8 to September 15, 2019) in Chengdu, China, in this study to compare three NO₂ measurement techniques: cavity ring-down spectroscopy (CRDS), photolytic conversion-chemiluminescence detector (PC-CLD), and cavity-enhanced absorption spectroscopy (CEAS). The results obtained from these three instruments were consistent throughout the entire dataset. Various interference factors were quantitatively analyzed that demonstrated the nitrous acid photolysis impact on the PC-CLD fluorescence signal and the influence of aldehyde absorption on the optical cavity technology were negligible under actual field conditions. Under high ozone pollution and high particulate pollution conditions, the results indicated that the three instruments reliably obtained NO₂ data under this complex air pollution environment. Some deviations might have occurred during high temperature conditions, the extent of overestimation was dependent on the photochemical age of an air mass defined as -log₁₀(NO_x/NO_y). PC-CLD tended to exhibit an overestimation of nearly 20 % when the -log₁₀(NO_x/NO_y) exceeded 0.5, and a portion of this overestimation could be attributed to peroxy nitrates. In the future, further comparisons among various NO₂ measurement techniques is meaningful to analyze potential interferences and improve atmospheric chemistry comprehension.