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

The family of atmospheric oxides of nitrogen, NO (e.g., nitrogen oxides (NO) + nitric acid (HNO) + nitrous acid (HONO) + peroxyacetyl nitrate (PAN) + particulate nitrate (pNO) + other), have an influential role in atmospheric chemistry, climate, and the environment. The nitrogen (δN) and oxygen (δO and ΔO) 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 δN, δO, and ΔO. 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 (NO). The laboratory tests indicate complete NO capture for the targeted concentration of 15 ppb for at least 24 h collections at 10 liters per minute, with δN and δO precisions of ±1.3‰ and 1.0‰, respectively, and minimal (2.2% ± 0.1%) NO collection on upstream denuders utilized for the capture of HNO and other acidic gases. The multispecies NO collection system showed excellent concentration correlations with online instrumentation for both HNO and NO and isotope reproducibility of ±1.7‰, ±1.8‰, and ±0.7‰ for δN, δO, and ΔO, respectively, for replicate experiments and highly time-resolved collections. This work demonstrates a new method that can enable the simultaneous collection of HNO and NO for accurate quantification of concentration and isotopic composition.