Gas sensors are identified as emerging devices for indicative measurements as defined in the European Directive for Air Quality (2008/50/EC, 2008). Compared to reference measurements, gas sensors would allow air pollution monitoring at lower cost. Recent development in sensors platforms mainly focused on the use of amperometric sensors (Mead et al., 2013 and Castell et al., 2013) because of the high linearity of their response and their limited drift over time. Conversely, this type of sensors suffers from a lack of selectivity that makes especially difficult to distinguish between ozone (O3) and nitrogen dioxide (NO2) (Spinelle et al., 2014.). Their wide application is also limited by their relative high price and short life time. On the contrary, Metal Oxides sensors (MOx) can be easily manufactured resulting in a moderate price. Unfortunately, MOx sensors have been shown by experiment to be difficult to calibrate because of their lack of linearity and their dependence on interfering variables as for example temperature and humidity (Gerboles and Buzica, 2009). Moreover, the stability of their calibration function over long period (longer than 100 days) is also a limitation to their applicability in field studies (Spinelle et al., 2015). Conversely, MOx sensors appear to be enough sensitive for monitoring inorganic gases in ambient air (Aleixandre and Gerboles, 2012).
In this paper we present an accurate evaluation of MOx sensors including commercial sensors and laboratory prototypes for monitoring O3 in ambient air at ppb level in order to give quantitative estimation of the effect of several parameters on sensor measurements. The list of sensors consisted of: O3 Sens 3000 (Unitec – IT), NanoEnvi (Ingenieros Assessores - SP), MiCS 2610 and Oz-47 (SGX Sensotech - CH), SP-61 (FIS – JP) and a prototype of WO3 sensor designed by IMN2P (FR).
Experiments were conducted in a laboratory exposure chamber and were designed to evaluate several metrological parameters: response time, sensitivity, repeatability, limit of detection, short term drift (over 3 days), long term drift (over more than 100 days), interference from gaseous compounds (NO2, NO, CO, CO2, NH3), differences of sensor values when measuring mixtures diluted with indoor, outdoor or filtered air and the effect of change of temperature and humidity. Additionally, the presence of hysteresis in sensor responses when changing O3 concentration levels, temperature or humidity was studied. The experimental design follows the Protocol of evaluation of low-cost gas sensors for air pollution (Spinelle et al., 2013). Precise set up of experiments and details of the data treatment are given in this protocol. A discussion of the experimental results allows advising which parameters needs attention, correction or control. An attempt of estimating the sensor measurement uncertainty from laboratory experiment is also carried out.
SPINELLE Laurent;
GERBOLES Michel;
ALEIXANDRE Manuel;
BONAVITACOLA Fausto;
2016-11-30
ITALIAN ASSOCIATION OF CHEMICAL ENGINEERING - AIDIC
JRC101975
1974-9791,
http://www.aidic.it/cet/16/54/054.pdf,
https://publications.jrc.ec.europa.eu/repository/handle/JRC101975,
10.3303/CET1654054,
