# Simultaneous detection of ozone and nitrogen dioxide by oxygen anion chemical ionization mass spectrometry: a fast-time-response sensor suitable for eddy covariance measurements

We report on the development, characterization, and field deployment of a fast-time-response sensor for measuring ozone (inline-formulaO3) and nitrogen dioxide (inline-formulaNO2) concentrations utilizing chemical ionization time-of-flight mass spectrometry (CI-ToFMS) with oxygen anion (inline-formula $M3inlinescrollmathmlchem{\mathrm{normal O}}_{normal 2}^{-}$ 17pt16ptsvg-formulamathimg26d368ad2bb5d49e9b215b03d31563a9 amt-13-1887-2020-ie00001.svg17pt16ptamt-13-1887-2020-ie00001.png ) reagent ion chemistry. We demonstrate that the oxygen anion chemical ionization mass spectrometer (Ox-CIMS) is highly sensitive to both inline-formulaO3 (180 counts sinline-formula−1 pptvinline-formula−1) and inline-formulaNO2 (97 counts sinline-formula−1 pptvinline-formula−1), corresponding to detection limits (inline-formula3σ, 1 s averages) of 13 and 9.9 pptv, respectively. In both cases, the detection threshold is limited by the magnitude and variability in the background determination. The short-term precision (1 s averages) is better than 0.3 % at 10 ppbv inline-formulaO3 and 4 % at 10 pptv inline-formulaNO2. We demonstrate that the sensitivity of the inline-formulaO3 measurement to fluctuations in ambient water vapor and carbon dioxide is negligible for typical conditions encountered in the troposphere. The application of the Ox-CIMS to the measurement of inline-formulaO3 vertical fluxes over the coastal ocean, via eddy covariance (EC), was tested during the summer of 2018 at Scripps Pier, La Jolla, CA. The observed mean ozone deposition velocity (inline-formulavd(inline-formulaO3)) was 0.013 cm sinline-formula−1 with a campaign ensemble limit of detection (LOD) of 0.0027 cm sinline-formula−1 at the 95 % confidence level, from each 27 min sampling period LOD. The campaign mean and 1 standard deviation range of inline-formulaO3 mixing ratios was inline-formula41.2±10.1 ppbv. Several fast ozone titration events from local NO emissions were sampled where unit conversion of inline-formulaO3 to inline-formulaNO2 was observed, highlighting instrument utility as a total odd-oxygen (inline-formula $M23inlinescrollmathmlchem{\mathrm{normal O}}_{x}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}{\mathrm{normal O}}_{normal 3}\phantom{\rule{0ex}{0ex}}+\phantom{\rule{0ex}{0ex}}{\mathrm{normal NO}}_{normal 2}$ 75pt13ptsvg-formulamathimgd5b8caa296edd90f045d885f0525d6c6 amt-13-1887-2020-ie00002.svg75pt13ptamt-13-1887-2020-ie00002.png ) sensor. The demonstrated precision, sensitivity, and time resolution of this instrument highlight its potential for direct measurements of inline-formulaO3 ocean–atmosphere and biosphere–atmosphere exchange from both stationary and mobile sampling platforms.

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Zitierform:

Novak, Gordon A. / Vermeuel, Michael P. / Bertram, Timothy H.: Simultaneous detection of ozone and nitrogen dioxide by oxygen anion chemical ionization mass spectrometry: a fast-time-response sensor suitable for eddy covariance measurements. 2020. Copernicus Publications.

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Rechteinhaber: Gordon A. Novak et al.

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