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

The family of atmospheric oxides of nitrogen, NOy (e.g., nitrogen oxides (NOx) + 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 (615N) and oxygen (618O and Delta 17O) stable isotopes of NOy 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 NOy, to accurately quantify 615N, 618O, and Delta 17O. This work presents controlled laboratory experiments and complex chamber a-pinene/NOx oxidation experiments of a sampling apparatus constructed for the simultaneous capture of multiple NOy species for isotope analysis using a series of coated denuders, with a focus on nitrogen dioxide (NO2 center dot). The laboratory tests indicate complete NO2 center dot capture for the targeted concentration of 15 ppbv for at least 24 h collections at 10 liters per minute, with 615N and 618O precisions of +/- 1.3 parts per thousand and 1.0 parts per thousand, respectively, and minimal (2.2% +/- 0.1%) NO2 center dot collection on upstream denuders utilized for the capture of HNO3 and other acidic gases. The multispecies NOy collection system showed excellent concentration correlations with online instrumentation for both HNO3 and NO2 center dot and isotope reproducibility of +/- 1.7 parts per thousand, +/- 1.8 parts per thousand, and +/- 0.7 parts per thousand for 615N, 618O, and Delta 17O, 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 center dot for accurate quantification of concentration and isotopic composition.

Automated summary

The family of atmospheric oxides of nitrogen, NOy, plays an influential role in atmospheric chemistry, climate, and the environment. The nitrogen and oxygen stable isotopes of NOy have the potential to track emission sources and quantify oxidation chemistry. This study presents a new method using a sampling apparatus to simultaneously capture multiple NOy species for accurate measurement of concentration and isotopic composition.