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Atmospheric HONO mixing ratios in indoor and outdoor environments span a range of less than a few parts per trillion by volume (pptv) up to tens of parts per billion by volume (ppbv) in combustion plumes. Previous HONO calibration sources have utilized proton transfer acid displacement from nitrite salts or solutions, with output that ranges from tens to thousands of ppbv. Instrument calibrations have thus required large dilution flows to obtain atmospherically relevant mixing ratios. Here we present a simple universal source to reach very low HONO calibration mixing ratios using a nitrite-coated reaction device with the addition of humid air and/or HCl from a permeation device. The calibration source developed in this work can generate HONO across the atmospherically relevant range and has high purity (> 90 %), reproducibility, and tunability. Mixing ratios at the tens of pptv level are easily reached with reasonable dilution flows. The calibration source can be assembled to start producing stable HONO mixing ratios (relative standard error, RSE ≤ 2 %) within 2 h, with output concentrations varying ≤ 25 % following simulated transport or complete disassembly of the instrument and with ≤ 10 % under ideal conditions. The simplicity of this source makes it highly versatile for field and lab experiments. The platform facilitates a new level of accuracy in established instrumentation, as well as intercomparison studies to identify systematic HONO measurement bias and interferences. [ABSTRACT FROM AUTHOR]

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 (Nr = all nitrogen compounds except for N2 and N2O) focus on gas-phase nitrogen and very few studies directly discuss the instrument capacity to measure the mass of Nr-containing particles. Here, we investigate the mass quantification of particle-bound nitrogen using a custom Nr system that involves total conversion to nitric oxide (NO) across platinum and molybdenum catalysts followed by NO-O3 chemiluminescence detection. We evaluate the particle conversion of the Nr instrument by comparing to mass derived concentrations of size-selected and counted ammonium sulfate ((NH4)2SO4), ammonium nitrate (NH4NO3), ammonium chloride (NH4Cl), sodium nitrate (NaNO3), and ammonium oxalate ((NH4)2C2O4) particles determined using instruments that measure particle number and size. These measurements demonstrate Nr-particle conversion across the Nr 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 CO2 across the instrument's platinum catalyst followed by a non-dispersive infrared (NDIR) CO2 detector. We show the Nr system is an accurate particle mass measurement method and demonstrate its ability to calibrate particle mass measurement instrumentation using single component, laboratory generated, Nr-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 (R² = 0.99) of particle mass measured as Nr with PILS-ESI/MS measurements converted to the corresponding particle anion mass (e.g. nitrate, sulfate, and chloride). The Nr and PILS-ESI/MS are shown to agree to within ~ 6 % for particle mass loadings 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 Nr 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. [ABSTRACT FROM AUTHOR]