Development and application of a nitrogen oxides analyzer based on the cavity attenuated phase shift technique.

Nitrogen oxides (NO) are crucial in tropospheric photochemical ozone (O) production and oxidation capacity. Currently, the widely used NO measurement technique is chemiluminescence (CL) (CL-NO), which tends to overestimate NO due to atmospheric oxidation products of NO (i.e., NO). We developed and characterized a NO measurement system using the cavity attenuated phase shift (CAPS) technique (CAPS-NO), which is free from interferences with nitrogen-containing species. The NO measured by the CAPS-NO and CL-NO analyzers were compared. Results show that both analyzers showed consistent measurement results for NO, but the NO measured by the CAPS-NO analyzer (NO) was mostly lower than that measured by the CL-NO analyzer (NO), which led to the deviations in O formation sensitivity regime and O (= O + NO) sources (i.e., regional background and photochemically produced O) determined by the ozone production efficiencies (OPE) calculated from NO and NO. Overall, OPE exceeded OPE by 18.9%, which shifted 3 out of 13 observation days from the VOCs-limited to the transition regime when judging using OPE, as compared to calculations using OPE. During the observation period, days dominated by regional background O accounted for 46% and 62% when determined using NO and NO, respectively. These findings suggest that the use of the CL-NO analyzer tends to underestimate both the VOCs-limited regime and the regional background Ox dominated days. The newly built CAPS-NO analyzer here can promote the accurate measurement of NO, which is meaningful for diagnosing O formation regimes and O sources.