Quantification of Organic Nitrates Using Thermal Dissociation Broadband Cavity-Enhanced Absorption Spectroscopy:...

Peroxy nitrates (RO₂NO₂, PNs) and alkyl nitrates (RONO₂, ANs) constitute the dominant fraction of atmospheric organic nitrates (ONs), playing crucial roles in nitrogen cycling and secondary organic aerosol (SOA) formation. Conventional quantification methods based on thermal dissociation coupled with nitrogen dioxide (NO₂) detection (TD-NO₂) are subject to significant interferences from secondary reactions. In this study, we report a dual-channel thermal dissociation broadband cavity-enhanced absorption spectroscopy (TD-BBCEAS) system for interference-suppressed measurement of ΣPNs and ΣANs. Two TD inlets operate at 180 °C (decomposing ΣPNs to NO₂ + RO₂ radicals) and 360 °C (decomposing ΣANs to NO₂ + RO radicals), achieving >99% TD efficiency while ensuring effective separation between ΣPNs and ΣANs. The BBCEAS-NO₂ measurement module improves the accuracy of NO₂ quantification by broadband spectral fitting (435-455 nm). The detection limits for ΣPNs and ΣANs were determined to be 18 and 21 pptv (60s, 3σ), respectively. Crucially, NO_x interferences were suppressed by (1) converting NO to NO₂ via ozone (O₃) addition to eliminate NO oxidation interference and (2) packing quartz wool to enhance radical collision losses, thereby inhibiting NO₂ recombination. Laboratory mixed-gas experiments confirmed stable PN/AN responses under variable NO_x levels, validating effective interference suppression. Field observation in Hefei showed excellent agreement (R² = 0.92) between the sum of ΣPNs, ΣANs, and NO_x measured by TD-BBCEAS and total reactive nitrogen (NO_y) from a commercial analyzer, accounting for 96% of NO_y. This result further validates the feasibility of measuring ΣPNs and ΣANs.