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

Abstract

We report on the development, characterization, and field deployment of a fast-time-response sensor for measuring ozone (O 3 ) and nitrogen dioxide (NO 2 ) concentrations utilizing chemical ionization time-of-flight mass spectrometry (CI-ToFMS) with oxygen anion (O − 2 ) reagent ion chemistry. We demonstrate that the oxygen anion chemical ionization mass spectrometer (Ox-CIMS) is highly sensitive to both O 3 (180 counts s −1 pptv −1 ) and NO 2 (97 counts s −1 pptv −1 ), corresponding to detection limits (3σ , 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 O 3 and 4 % at 10 pptv NO 2 . We demonstrate that the sensitivity of the O 3 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 O 3 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 (v d (O 3 )) was 0.013 cm s −1 with a campaign ensemble limit of detection (LOD) of 0.0027 cm s −1 at the 95 % confidence level, from each 27 min sampling period LOD. The campaign mean and 1 standard deviation range of O 3 mixing ratios was 41.2 ± 10.1 ppbv. Several fast ozone titration events from local NO emissions were sampled where unit conversion of O 3 to NO 2 was observed, highlighting instrument utility as a total odd-oxygen (O x = O 3 + NO 2 ) sensor. The demonstrated precision, sensitivity, and time resolution of this instrument highlight its potential for direct measurements of O 3 ocean-atmosphere and biosphere-atmosphere exchange from both stationary and mobile sampling platforms.

A Cavity-Enhanced UV Absorption Instrument for High Precision, Fast Time Response Ozone Measurements

“…The observational records of terrestrial (O3) are limited in number and do not capture the full variability in O3 deposition rates with land cover (Clifton et al, 2020a). Furthermore, studies of O3 deposition to the ocean (e.g., Kawa and Pearson, 1989;Faloona et al, 2005;Helmig et al, 2012;Novak et al, 2020) report deposition velocities of ~ 0.01-0.05 cm s-1, which are 1-2 orders of magnitude lower than typical 30 terrestrial values. Observations from Helmig et al (2012) and Novak et al (2020) also suggest that O3 deposition may vary with sea surface temperature.…”

A cavity-enhanced ultraviolet absorption instrument for high-precision, fast-time-response ozone measurements

“…The observational records of terrestrial v d (O 3 ) are limited in number and do not capture the full variability in O 3 deposition rates with land cover (Clifton et al, 2020a). Furthermore, studies of O 3 deposition to the ocean (e.g., Kawa and Pearson, 1989;Faloona et al, 2005;Helmig et al, 2012;Novak et al, 2020) report deposition velocities of ∼ 0.01-0.05 cm s −1 , which are 1-2 orders of magnitude lower than typical terrestrial values. Observations from Helmig et al (2012) also suggest that O 3 deposition may vary with sea surface temperature.…”

“…Global chemistry modeling frameworks that incorporate O 3 dry deposition (e.g., Bey et al, 2001;Lamarque et al, 2012) often apply fixed deposition rates to the ocean and heavily param-eterized deposition schemes over land (Wesely, 1989). However, process-level representation of O 3 deposition improves agreement between modeled and observed surface O 3 concentrations (Clifton et al, 2020b;Pound et al, 2020). The range and variability in O 3 deposition rates thus motivates the need for further v d (O 3 ) measurements to refine both atmospheric and land surface model predictions.…”

“…The EC technique demands fast-time-response, high-precision sensors to resolve the turbulence-driven variability in scalar concentrations. O 3 fluxes are therefore measured using highly sensitive O 3 detection methods such as chemiluminescence (e.g., Bariteau et al, 2010;Muller et al, 2010) and, more recently, chemical ionization mass spectrometry (CIMS) (Novak et al, 2020). Chemiluminescence detectors employ either nitric oxide (NO) gas or organic dyes, which generate photons on reaction with O 3 .…”

“…While these instruments exhibit good sensitivity, they have practical drawbacks involving the use of cylinders containing toxic compressed gases or dangerous chemical dyes. Novak et al (2020) successfully demonstrated the use of oxygen anion CIMS to measure O 3 and its vertical fluxes with a detection limit of <0.005 cm s −1 over the ocean. To the best of our knowledge, ultraviolet (UV) absorption instruments have not previously been utilized for O 3 flux measurements due to insufficient sensitivity (e.g., Gao et al, 2012).…”