Evaluation of low-cost electro-chemical sensors for environmental monitoring of ozone, nitrogen dioxide, and carbon monoxide

• Published in: Journal of occupational and environmental hygiene Vol. 15; no. 2; pp. 87 - 98
• Main Authors: Afshar-Mohajer, Nima, Zuidema, Christopher, Sousan, Sinan, Hallett, Laura, Tatum, Marcus, Rule, Ana M., Thomas, Geb, Peters, Thomas M., Koehler, Kirsten
• Format: Journal Article
• Language: English
• Published: England Taylor & Francis 01-02-2018
• Subjects: Air Pollutants - analysis; Air quality; Carbon Monoxide - analysis; Electrochemical Techniques - economics; Electrochemical Techniques - instrumentation; Environmental Monitoring - economics; Environmental Monitoring - instrumentation; field calibration; gas sensors; monitoring network; Nitrogen Dioxide - analysis; Ozone - analysis; monitoring network; Air quality; field calibration; gas sensors
• ISSN: 1545-9624; 1545-9632
• DOI: 10.1080/15459624.2017.1388918

Development of an air quality monitoring network with high spatio-temporal resolution requires installation of a large number of air pollutant monitors. However, state-of-the-art monitors are costly and may not be compatible with wireless data logging systems. In this study, low-cost electro-chemical sensors manufactured by Alphasense Ltd. for detection of CO and oxidative gases (predominantly O
3
and NO
2
) were evaluated. The voltages from three oxidative gas sensors and three CO sensors were recorded every 2.5 sec when exposed to controlled gas concentrations in a 0.125-m
3
acrylic glass chamber. Electro-chemical sensors for detection of oxidative gases demonstrated sensitivity to both NO
2
and O
3
with similar voltages recorded when exposed to equivalent environmental concentrations of NO
2
or O
3
gases, when evaluated separately. There was a strong linear relationship between the recorded voltages and target concentrations of oxidative gases (R
2
> 0.98) over a wide range of concentrations. Although a strong linear relationship was also observed for CO concentrations below 12 ppm, a saturation effect was observed wherein the voltage only changes minimally for higher CO concentrations (12-50 ppm). The nonlinear behavior of the CO sensors implied their unsuitability for environments where high CO concentrations are expected. Using a manufacturer-supplied shroud, sensors were tested at 2 different flow rates (0.25 and 0.5 Lpm) to mimic field calibration of the sensors with zero air and a span gas concentration (2 ppm NO2 or 15 ppm CO). As with all electrochemical sensors, the tested devices were subject to drift with a bias up to 20% after 9 months of continuous operation. Alphasense CO sensors were found to be a proper choice for occupational and environmental CO monitoring with maximum concentration of 12 ppm, especially due to the field-ready calibration capability. Alphasense oxidative gas sensors are usable only if it is valuable to know the sum of the NO
2
and O
3
concentrations.