Abstract
Abstract. 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.
Highlights
In the lower troposphere, the hydroxyl radical (OH) is the principal daytime gas-phase oxidant and will react with volatile organic compounds (VOCs) to form secondary pollutants such as ozone (O3) and secondary organic aerosols (Spataro and Ianniello, 2014; Ye et al, 2018)
Our results suggest that the use of water vapor passed over a NaNO2-coated PFA reaction device produces sub-ppbv mixing ratios of HONO for calibration of instruments making ambient observations in remote environments
We present a cost-effective, portable, stable, tunable, and robust gas-phase HONO calibration source
Summary
The hydroxyl radical (OH) is the principal daytime gas-phase oxidant and will react with volatile organic compounds (VOCs) to form secondary pollutants such as ozone (O3) and secondary organic aerosols (Spataro and Ianniello, 2014; Ye et al, 2018). Photolysis of nitrous acid (HONO) is a direct source of the hydroxyl radical (OH) (Reaction R1). This can be a significant contributor to the integrated daily OH budget, ranging from 4 % to 56 % in urban areas (Lee et al, 2013; Volkamer et al, 2010) up to 80 % in semirural areas in the winter (Kim et al, 2014), along with additional vertical and temporal variability (Crilley et al, 2016; Young et al, 2012; Zhang et al, 2009). There is a growing body of evidence that HONO concentrations can be significant in indoor
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