CO2 and CH4 measurements in ambient air : testing of two low-cost sensors in temperature controlled measuring chamber of AirSensEUR

The AirSensEURs equipped with temperature controlled measuring chamber set to 40 °C were tested at the JRC observatory station to measure CO2 and CH4 in air. The Picarro measurements were used as reference data for calibration of sensors and their prediction performance. For CO2, multiple linear model with water vapour and air pressure in the measuring chamber as covariates was used for calibration. The performance of sensors was evaluated for the capacity to achieve the data quality objective (DQO), which is expanded measurement uncertainty of 10 ppm at 500 ppm of CO2. The temperature of chamber was maintained at set value with good accuracy. The K96 sensors were met or close to meet the DQO when the longest path length was used. The least sensitive shorter path length yielded significantly worse performance. The K96 sensors showed a notable drift which did not associate with any measured parameter. The D300 sensor was not able to meet the DQO. The K96 sensors were not able to detect CH4 in air. Further tests are required to examine the efficiency of temperature control, the sensor accuracy and drift, in every season.