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