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

Area of Science:

• Atmospheric Chemistry
• Air Quality Monitoring
• Analytical Instrumentation

Background:

• Nitrogen oxides (NOx) are key to tropospheric ozone production and atmospheric oxidation.
• Conventional chemiluminescence (CL-NOx) methods often overestimate NO2 due to interferences from other nitrogen species.
• Accurate NOx measurements are critical for understanding air quality and ozone pollution dynamics.

Purpose of the Study:

• To develop and validate a novel NOx measurement system using cavity attenuated phase shift (CAPS-NOx) technology.
• To compare the performance of the CAPS-NOx system against the standard CL-NOx technique.
• To assess the impact of measurement differences on the determination of ozone formation regimes and ozone (Ox) sources.

Main Methods:

• Development and characterization of a CAPS-NOx analyzer.
• Comparative analysis of NOx, NO, and NO2 measurements between CAPS-NOx and CL-NOx analyzers.
• Calculation and comparison of ozone production efficiencies (OPE) and identification of Ox source contributions using data from both methods.

Main Results:

• Both CAPS-NOx and CL-NOx analyzers provided consistent NO measurements.
• The CAPS-NOx analyzer consistently measured lower NO2 concentrations compared to the CL-NOx analyzer.
• Ozone production efficiencies calculated using CL-NOx data were higher (18.9%) than those from CAPS-NOx, leading to shifts in ozone formation regime classification for 3 out of 13 days.
• The proportion of days dominated by regional background Ox was higher when determined by CAPS-NOx (62%) versus CL-NOx (46%).

Conclusions:

• The CL-NOx method tends to underestimate the prevalence of VOCs-limited ozone formation regimes and regional background Ox contributions.
• The developed CAPS-NOx system offers improved accuracy in NO2 measurement, crucial for precise diagnosis of ozone formation pathways.
• Accurate NOx measurements are essential for effective air quality management and pollution control strategies.