Efficacy of Paired Electrochemical Sensors for Measuring Ozone Concentrations
Creators: name: Zuidema, Christopher
name: Afshar-Mohajer, Nima
name: Tatum, Marcus
name: Geb Thomas
name: Peters, Thomas
name: Koehler, Kirsten
Publisher: name: Taylor & Francis
Year: 2019
Subjects: subject: Space Science
subject: Medicine
subject: Molecular Biology
subject: 59999 Environmental Sciences not elsewhere classified
subject: FOS: Earth and related environmental sciences
subject: FOS: Earth and related environmental sciences
subject: 39999 Chemical Sciences not elsewhere classified
subject: FOS: Chemical sciences
subject: FOS: Chemical sciences
subject: 69999 Biological Sciences not elsewhere classified
subject: FOS: Biological sciences
subject: FOS: Biological sciences

description: Typical low-cost electrochemical sensors for ozone (O<sub>3</sub>) are also highly responsive to nitrogen dioxide (NO<sub>2</sub>). Consequently, a single sensor’s response to O<sub>3</sub> is indistinguishable from its response to NO<sub>2</sub>. Recently, a method for quantifying O<sub>3</sub> concentrations became commercially available (Alphasense Ltd., Essex, UK): collocating a pair of sensors, a typical oxidative gas sensor that responds to both O<sub>3</sub> and NO<sub>2</sub> (model OX-B431) and a second similar sensor that filters O<sub>3</sub> and responds only to NO<sub>2</sub> (model NO2-B43F). By pairing the two sensors, O<sub>3</sub> concentrations can be calculated. We calibrated samples of three NO2-B43F sensors and three OX-B431 sensors with NO<sub>2</sub> and O<sub>3</sub> exclusively and conducted mixture experiments over a range of 0–1.0 ppm NO<sub>2</sub> and 0–125 ppb O<sub>3</sub> to evaluate the ability of the paired sensors to quantify NO<sub>2</sub> and O<sub>3</sub> concentrations in mixture. Although the slopes of the response among our samples of three sensors of each type varied by as much as 37%, the individual response of the NO2-B43F sensors to NO<sub>2</sub> and OX-B431 sensors to NO<sub>2</sub> and O<sub>3</sub> were highly linear over the concentrations studied (R<sup>2</sup> ≥ 0.99). The NO2-B43F sensors responded minimally to O<sub>3</sub> gas with statistically non-significant slopes of response. In mixtures of NO<sub>2</sub> and O<sub>3</sub>, quantification of NO<sub>2</sub> was generally accurate with overestimates up to 29%, compared to O<sub>3</sub>, which was generally underestimated by as much as 187%. We observed changes in sensor baseline over 4 days of experiments equivalent to 34 ppb O<sub>3</sub>, prompting an alternate method of calculating concentrations by baseline-correcting sensor signal. The baseline-correction method resulted in underestimates of NO<sub>2</sub> up to 44% and decreases in the underestimation of O<sub>3</sub> up to 107% for O<sub>3</sub>. Both methods for calculating gas concentrations progressively underestimated O<sub>3</sub> concentrations as the ratio of NO<sub>2</sub> signal to O<sub>3</sub> signal increased. Our results suggest that paired NO2-B43F and OX-B431 sensors permit quantification of NO<sub>2</sub> and O<sub>3</sub> in mixture, but that O<sub>3</sub> concentration estimates are less accurate and precise than those for NO<sub>2</sub>.