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

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 2months 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

Intra-urban spatial variability of surface ozone and carbon dioxide in Riverside, CA: viability and validation of low-cost sensors

“…Researchers also deployed these gas semiconductor sensors in British Columbia over roughly 10,000 km 2 for three months finding low errors (3 +/-2 ppb) between hourly averaged sensor and reference instruments while documenting the challenges of using, in this instance, wireless sensor networks (Bart et al, 2014). Lin and coworkers demonstrated high correlations (0.91) between tungsten oxide semiconductor ozone sensors and hourly averaged Federal Reference Method (FRM) chemiluminescence gas 25 analyzer measurements in Edinburgh, UK with similar magnitudes (Lin et al, 2015).…”

“…The current spacing is not sufficient to capture high spatial resolution concentrations (Bart et al, 2014;Moltchanov et al, 2015). Additionally, this variability could potentially be used to inform exposure assessment for health studies as well as improve our understanding of pollutant sources and fate (Simon et al, 2016;Lin et al, 2015;Blanchard et 10 al., 2014).…”

Characteristics and applications of small, portable gaseous air pollution monitors

“…These three gases are common criteria urban air pollutants that have been widely analyzed in the recent scientific literature and can be harmful to human health (e.g. Castell et al, 2013;Deville Cavellin et al, 2015;Good et al, 2015;Lin et al, 2015). The air pollution monitors were chosen based upon the availability and accessibility of the comparable information.…”

“…Furthermore, while numerous research studies and reviews have been published on the use of such mobile and personalized monitors for particulate matter, information on the use of mobile monitors for gaseous pollutants is scarce. Studies have distinguished the technologies of mobile monitors of gaseous pollutants from those of stationary monitors (Kumar et al, 2015;Aleixandre and Gerboles, 2012;Castell et al, 2013;Steinle et al, 2013;Snyder et al, 2013;Van Poppel et al, 2013) and evaluated mobile monitors in comparison to reference analyzers (Gerboles and Buzica, 2009;Lin et al, 2015;Williams et al, 2014b), yet no current study synthesizes these findings or promotes new research directions from the perspectives of specific audiences and intended applications. Therefore, this state-of-the-art review is the first to provide an exclusive assessment of small portable air pollution monitors that measure ambient gaseous outdoor pollutants.…”

“…The monitor's base allows for the user to employ one of many sensor heads, each designed to measure an individual gas. It has been shown that the ozone sensor head is the most effective when compared to a reference analyzer (Lin et al, 2015;MacDonald et al, 2014) and that other sensor heads need corrections in order to have similar accuracy (Lin et al, 2015). A recent research study employed both NO 2 and O 3 monitors to develop a land-use regression model and exposure surfaces in a large city (Deville Cavellin et al, 2015), demonstrating the ability of this monitor to obtain useful spatial and temporal information about urban air pollution.…”