Quantification of Organic Nitrates Using Thermal Dissociation Broadband Cavity-Enhanced Absorption Spectroscopy: Interference Suppression and Atmospheric Measurement.

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, NOx 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 NOx levels, validating effective interference suppression. Field observation in Hefei showed excellent agreement (R2 = 0.92) between the sum of ΣPNs, ΣANs, and NOx measured by TD-BBCEAS and total reactive nitrogen (NOy) from a commercial analyzer, accounting for 96% of NOy. This result further validates the feasibility of measuring ΣPNs and ΣANs.