Protocol of evaluation and calibration of low-cost gas sensors for the monitoring of air pollution

Metrology for Chemical Pollutants in Air (MACPoll) is a joint research project of the European Metrology Research Programme of EURAMET that among other activities deals with low- cost gas sensors for air quality monitoring. Gas sensors are identified as emerging measuring devices for "indicative measurements" regulated in the Air Quality Directive. Compared to reference measurements, gas sensors would allow air pollution monitoring at a lower cost. The Directive allows using indicative measurements without restriction in the zones where the upper assessment threshold (UAT) is not exceeded while they permit a reduction of 50 % of the minimum reference measurements where the UAT is exceeded. The Directive does not specify any indicative method but it requires to demonstrate that they can meet a data quality objective (DQO) that is about twice less stringent than the one of reference methods. The DQO is defined as a relative expanded uncertainty. Since the Directive does not give any guidance for this demonstration, within MACPoll it has been decided to draft a protocol for the evaluation of gas sensors.