Reactive nitrogen species are emitted into the atmosphere from a variety of sources, including vehicles, biomass burning, agriculture, and industry. Ultimately, these reactive nitrogen species and their products have implications for quality of air, soil, water, and human health. Nitric acid (HNO3) gas is most often a secondary product, existing in equilibrium with the particle phase. Speciation between the two phases is essential to understanding the chemistry of the atmospheric environment, and isotopes add a unique dimension of being able to track oxidation chemistry and primary emission sources. However, it is critical to determine the suitability of collection methods for consistent isotopic results that accurately reflect environmental values. Honeycomb denuders, coated with a selective solution, allows for capture of the gas phase while particles (&lt;2.5 µm) continue downstream and collect on a Nylon filter. The literature debates the merit of using a Na2CO3 coating on denuders as it is more efficient for the collection of many acidic species, versus a NaCl coating, which may be more selective for strong acids. Neither of these methods, nor the use of Nylon filters to collect particulate nitrate (pNO3-), have been evaluated for quantitative determination of stable isotope ratios (15N/14N; 18O/16O). Evaluation and comparison of a Na2CO3 and a NaCl denuder coating for collection efficiency, operative capacity, and quantitative collection of isotopes was conducted. The Na2CO3 showed high operative capacity at 1,600 µg or 39.4 ppbv HNO3(g) over 24 h, but showed lower selectivity in comparison to the NaCl coating. The NaCl coating has a much lower operative capacity at 76 µg or 1.9 ppbv HNO3(g) over 24 h. Nylon Filters have been shown previously to collect pNO3- quantitatively, and our results agree. Overall, both coating solutions and nylon filters yield highly reproducible isotopic results; showing no isotopic fractionation as a result of collection.

Collection and speciation of gaseous and particulate nitrate for isotopic determination

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.