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 r = all nitrogen compounds except for N 2 and N 2 O) focus on gas-phase nitrogen and very few studies directly discuss the instrument capacity to measure the mass of N r -containing particles. Here, we investigate the mass quantification of particle-bound nitrogen using a custom N r system that involves total conversion to nitric oxide (NO) across platinum and molybdenum catalysts followed by NO−O 3 chemiluminescence detection. We evaluate the particle conversion of the N r instrument by comparing to mass-derived concentrations of size-selected and counted ammonium sulfate ((NH 4 ) 2 SO 4 ), ammonium nitrate (NH 4 NO 3 ), ammonium chloride (NH 4 Cl), sodium nitrate (NaNO 3 ), and ammonium oxalate ((NH 4 ) 2 C 2 O 4 ) particles determined using instruments that measure particle number and size. These measurements demonstrate N r -particle conversion across the N r 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 2 across the instrument's platinum catalyst followed by a nondispersive infrared (NDIR) CO 2 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 2 ). We show the N r system is an accurate particle mass measurement method and demonstrate its ability to calibrate particle mass measurement instrumentation using single-component, laboratory-generated, N r -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 ( R 2  = 0.99) of particle mass measured as N r with PILS–ESI/MS measurements converted to the corresponding particle anion mass (e.g., nitrate, sulfate, and chloride). The N r and PILS–ESI/MS are shown to agree to within ∼ 6 % for particle mass loadings of up to 120 µg m −3 . 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 r 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.