Measurements of total organic nitrates by thermal dissociation broadband cavity-enhanced absorption spectroscopy

Organic nitrates (ONs) are key atmospheric nitrogen-containing compounds that significantly influence nitrogen cycling and secondary organic aerosols (SOAs) formation. The quantification of each individual ONs is impractical given their structural diversity, chemical complexity, and low atmospheric abundance. Here we developed a thermal dissociation broadband cavity-enhanced absorption spectroscopy (TD-BBCEAS) system that utilizes the thermal stability of ONs to quantify the total ONs (ΣONs). Optimized thermal dissociation at 360 °C (determined via TD efficiency curve) achieved > 99% conversion of ΣONs to NO₂, which was subsequently quantified by BBCEAS. The detection limit for ΣONs is 14 pptv (60 s, 1σ). Comparing the TD-BBCEAS system with other instruments for NO₂ and EHN measurement, the results showed high consistency (R² = 0.999), verifying the reliability and accuracy of TD-BBCEAS system. The system was applied to the observation of actual atmospheric ΣONs from October to November 2024, and the data analysis results with a commercial NO_y analyzer showed that the sum of NO+NO₂+ΣONs was highly correlated with NO_y concentration (R² = 0.995), accounting for approximately 97%. This indicates the ability of the TD-BBCEAS system to accurately quantify ΣONs.