Collection of Nitrogen Dioxide for Nitrogen and Oxygen Isotope Determination─Laboratory and Environmental Chamber...

The family of atmospheric oxides of nitrogen, NO (e.g., nitrogen oxides (NO) + nitric acid (HNO₃) + nitrous acid (HONO) + peroxyacetyl nitrate (PAN) + particulate nitrate (pNO₃^-) + other), have an influential role in atmospheric chemistry, climate, and the environment. The nitrogen (δ¹⁵N) and oxygen (δ¹⁸O and Δ¹⁷O) stable isotopes of NO are novel tools for potentially tracking emission sources and quantifying oxidation chemistry. However, there is a lack of well-established methods, particularly for speciated gas-phase components of NO, to accurately quantify δ¹⁵N, δ¹⁸O, and Δ¹⁷O. This work presents controlled laboratory experiments and complex chamber α-pinene/NO oxidation experiments of a sampling apparatus constructed for the simultaneous capture of multiple NO species for isotope analysis using a series of coated denuders, with a focus on nitrogen dioxide (NO₂). The laboratory tests indicate complete NO₂^• capture for the targeted concentration of 15 ppb_v for at least 24 h collections at 10 liters per minute, with δ¹⁵N and δ¹⁸O precisions of ±1.3‰ and 1.0‰, respectively, and minimal (2.2% ± 0.1%) NO₂^• collection on upstream denuders utilized for the capture of HNO₃ and other acidic gases. The multispecies NO collection system showed excellent concentration correlations with online instrumentation for both HNO₃ and NO₂^• and isotope reproducibility of ±1.7‰, ±1.8‰, and ±0.7‰ for δ¹⁵N, δ¹⁸O, and Δ¹⁷O, respectively, for replicate experiments and highly time-resolved collections. This work demonstrates a new method that can enable the simultaneous collection of HNO₃ and NO₂^• for accurate quantification of concentration and isotopic composition.