Characterization of a catalyst-based conversion technique to measure total particulate nitrogen and organic carbon and comparison to a particle mass measurement instrument

The chemical composition of aerosol particles is a key aspect in determining their impact on the environment. For example, nitrogen-containing particles impact atmospheric chemistry, air quality, and ecological N deposition. Instruments that measure total reactive nitrogen (N<sub>r</sub&...

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Bibliographic Details
Main Authors: C. E. Stockwell, A. Kupc, B. Witkowski, R. K. Talukdar, Y. Liu, V. Selimovic, K. J. Zarzana, K. Sekimoto, C. Warneke, R. A. Washenfelder, R. J. Yokelson, A. M. Middlebrook, J. M. Roberts
Format: Article
Language:English
Published: Copernicus Publications 2018-05-01
Series:Atmospheric Measurement Techniques
Online Access:https://www.atmos-meas-tech.net/11/2749/2018/amt-11-2749-2018.pdf
Description
Summary:The chemical composition of aerosol particles is a key aspect in determining their impact on the environment. For example, nitrogen-containing particles impact atmospheric chemistry, air quality, and ecological N deposition. Instruments that measure total reactive nitrogen (N<sub>r</sub> = all nitrogen compounds except for N<sub>2</sub> and N<sub>2</sub>O) focus on gas-phase nitrogen and very few studies directly discuss the instrument capacity to measure the mass of N<sub>r</sub>-containing particles. Here, we investigate the mass quantification of particle-bound nitrogen using a custom N<sub>r</sub> system that involves total conversion to nitric oxide (NO) across platinum and molybdenum catalysts followed by NO−O<sub>3</sub> chemiluminescence detection. We evaluate the particle conversion of the N<sub>r</sub> instrument by comparing to mass-derived concentrations of size-selected and counted ammonium sulfate ((NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>), ammonium nitrate (NH<sub>4</sub>NO<sub>3</sub>), ammonium chloride (NH<sub>4</sub>Cl), sodium nitrate (NaNO<sub>3</sub>), and ammonium oxalate ((NH<sub>4</sub>)<sub>2</sub>C<sub>2</sub>O<sub>4</sub>) particles determined using instruments that measure particle number and size. These measurements demonstrate N<sub>r</sub>-particle conversion across the N<sub>r</sub> catalysts that is independent of particle size with 98 ± 10 % efficiency for 100–600 nm particle diameters. We also show efficient conversion of particle-phase organic carbon species to CO<sub>2</sub> across the instrument's platinum catalyst followed by a nondispersive infrared (NDIR) CO<sub>2</sub> detector. However, the application of this method to the atmosphere presents a challenge due to the small signal above background at high ambient levels of common gas-phase carbon compounds (e.g., CO<sub>2</sub>). We show the N<sub>r</sub> system is an accurate particle mass measurement method and demonstrate its ability to calibrate particle mass measurement instrumentation using single-component, laboratory-generated, N<sub>r</sub>-containing particles below 2.5 µm in size. In addition we show agreement with mass measurements of an independently calibrated online particle-into-liquid sampler directly coupled to the electrospray ionization source of a quadrupole mass spectrometer (PILS–ESI/MS) sampling in the negative-ion mode. We obtain excellent correlations (<i>R</i><sup>2</sup> = 0.99) of particle mass measured as N<sub>r</sub> with PILS–ESI/MS measurements converted to the corresponding particle anion mass (e.g., nitrate, sulfate, and chloride). The N<sub>r</sub> and PILS–ESI/MS are shown to agree to within ∼ 6 % for particle mass loadings of up to 120 µg m<sup>−3</sup>. Consideration of all the sources of error in the PILS–ESI/MS technique yields an overall uncertainty of ±20 % for these single-component particle streams. These results demonstrate the N<sub>r</sub> system is a reliable direct particle mass measurement technique that differs from other particle instrument calibration techniques that rely on knowledge of particle size, shape, density, and refractive index.
ISSN:1867-1381
1867-8548