Characterization of a catalyst-based total nitrogen and carbon conversion technique to calibrate particle mass measurement instrumentation

摘要

The chemical composition of aerosol particles is a key aspect in determining their impact on the environment. For example, nitrogen (N)-containing particles impact atmospheric chemistry, air quality, and ecological N-deposition. Instruments that measure total reactive nitrogen (N = all nitrogen compounds except for N and NO) focus on gas-phase nitrogen and very few studies directly discuss the instrument capacity to measure the mass of N–containing particles. Here, we investigate the mass quantification of particle-bound nitrogen using a custom N system that involves total conversion to nitric oxide (NO) across platinum and molybdenum catalysts followed by NO-O chemiluminescence detection. We evaluate the particle conversion of the N instrument by comparing to mass derived concentrations of size-selected and counted ammonium sulfate ((NH)SO), ammonium nitrate (NHNO), ammonium chloride (NHCl), sodium nitrate (NaNO), and ammonium oxalate ((NH)CO) particles determined using instruments that measure particle number and size. These measurements demonstrate N-particle conversion across the N catalysts that is independent of particle size with 98 ± 10 % efficiency for 100–600 nm particle diameters. We also show conversion of particle-phase organic carbon species to CO across the instrument’s platinum catalyst followed by a non-dispersive infrared (NDIR) CO detector. We show the N system is an accurate particle mass measurement method and demonstrate its ability to calibrate particle mass measurement instrumentation using single component, laboratory generated, N-containing particles below 2.5 µm in size. In addition we show agreement with mass measurements of an independently calibrated on-line 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 = 0.99) of particle mass measured as N with PILS-ESI/MS measurements converted to the corresponding particle anion mass (e.g. nitrate, sulfate, and chloride). The N and PILS-ESI/MS are shown to agree to within ~ 6 % for particle mass loadings up to 120 µg m. 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 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.