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

The family of atmospheric oxides of nitrogen, NO y (e.g., nitrogen oxides (NO x ) + nitric acid (HNO 3 ) + nitrous acid (HONO) + peroxyacetyl nitrate (PAN) + particulate nitrate (pNO 3 - ) + other), have an influential role in atmospheric chemistry, climate, and the environment. The nitrogen (δ 15 N) and oxygen (δ 18 O and Δ 17 O) stable isotopes of NO y 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 y , to accurately quantify δ 15 N, δ 18 O, and Δ 17 O. This work presents controlled laboratory experiments and complex chamber α-pinene/NO x oxidation experiments of a sampling apparatus constructed for the simultaneous capture of multiple NO y species for isotope analysis using a series of coated denuders, with a focus on nitrogen dioxide (NO 2 • ). The laboratory tests indicate complete NO 2 • capture for the targeted concentration of 15 ppb v for at least 24 h collections at 10 liters per minute, with δ 15 N and δ 18 O precisions of ±1.3‰ and 1.0‰, respectively, and minimal (2.2% ± 0.1%) NO 2 • collection on upstream denuders utilized for the capture of HNO 3 and other acidic gases. The multispecies NO y collection system showed excellent concentration correlations with online instrumentation for both HNO 3 and NO 2 • and isotope reproducibility of ±1.7‰, ±1.8‰, and ±0.7‰ for δ 15 N, δ 18 O, and Δ 17 O, respectively, for replicate experiments and highly time-resolved collections. This work demonstrates a new method that can enable the simultaneous collection of HNO 3 and NO 2 • for accurate quantification of concentration and isotopic composition.