Evaluation and calibration of Aeroqual series 500 portable gas sensors for accurate measurement of ambient ozone and nitrogen dioxide

C Lin,J Gillespie,M.D Schuder,W Duberstein,I.J Beverland,M.R Heal

doi:10.1016/j.atmosenv.2014.11.002

C Lin, J Gillespie + Show 4 more

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https://doi.org/10.1016/j.atmosenv.2014.11.002

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Abstract

Low-power, and relatively low-cost, gas sensors have potential to improve understanding of intra-urban air pollution variation by enabling data capture over wider networks than is possible with ‘traditional’ reference analysers. We evaluated an Aeroqual Ltd. Series 500 semiconducting metal oxide O3 and an electrochemical NO2 sensor against UK national network reference analysers for more than 2 months at an urban background site in central Edinburgh. Hourly-average Aeroqual O3 sensor observations were highly correlated (R2 = 0.91) and of similar magnitude to observations from the UV-absorption reference O3 analyser. The Aeroqual NO2 sensor observations correlated poorly with the reference chemiluminescence NO2 analyser (R2 = 0.02), but the deviations between Aeroqual and reference analyser values ([NO2]Aeroq − [NO2]ref) were highly significantly correlated with concurrent Aeroqual O3 sensor observations [O3]Aeroq. This permitted effective linear calibration of the [NO2]Aeroq data, evaluated using ‘hold out’ subsets of the data (R2 ≥ 0.85). These field observations under temperate environmental conditions suggest that the Aeroqual Series 500 NO2 and O3 monitors have good potential to be useful ambient air monitoring instruments in urban environments provided that the O3 and NO2 gas sensors are calibrated against reference analysers and deployed in parallel.

Highlights

Ozone (O3) and nitrogen dioxide (NO2) are very important air pollutants subject to mandatory air quality limits in many jurisdictions
The Aeroqual NO2 sensor observations correlated poorly with the reference chemiluminescence NO2 analyser (R2 = 0.02), but the deviations between Aeroqual and reference analyser values ([NO2]Aeroq – [NO2]ref) were highly significantly correlated with concurrent Aeroqual O3 sensor observations [O3]Aeroq. This permitted effective linear calibration of the [NO2]Aeroq data, evaluated using ‘hold out’ subsets of the data (R2 0.85). These field observations under temperate environmental conditions suggest that the Aeroqual Series 500 NO2 and O3 monitors have good potential to be useful ambient air monitoring instruments in urban environments provided that the O3 and NO2 gas sensors are calibrated against reference analysers and deployed in parallel
The Aeroqual and UV-absorbance reference analyser O3 data were highly correlated (R2 = 0.91, n = 1274), albeit with a trend for this Aeroqual O3 sensor to overestimate on average compared with the reference instrument when O3 concentrations from the latter exceeded ~43 μg m-3, and to underestimate on average for concentrations below a reference instrument O3 concentration of ~43 μg m-3 (e.g. 16 μg m-3 Aeroqual value for a reference instrument value of 20 μg m-3)

Summary

Introduction

Ozone (O3) and nitrogen dioxide (NO2) are very important air pollutants subject to mandatory air quality limits in many jurisdictions. The quality of the data generated by these monitors compared with established techniques remains a concern (Snyder et al, 2013), in particular interference in the sensing of NO2 by O3 (Williams et al, 2009; Mead et al, 2013). One such type of monitor is the Aeroqual Ltd. Series 500 ENV portable gas monitors (www.aeroqual.com/category/products/handheld-monitors). The Aeroqual monitors are a factor of approximately 5 to 10 times lower cost than standard air quality monitoring instrumentation for these gases

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