Use and evaluation of low cost sensors for the monitoring of NO2 and O3 in ambient air within the EURAMET MACPoll project

Metrology for chemical pollutants in air (MACPoll) is a EURAMET joint research project. It is divided into four work packages: NO2 and SO2 calibration zero gas (WP2) and span (WP1) at low concentration levels; development of reference methods/materials for semi-VOC in indoor air (WP3) and development/validation of micro-sensors (WP4). The aim of WP4 includes developing new graphene NO2 sensors and a standardized evaluation protocol for gas sensors, running an extended validation for the graphene sensor and other commercial sensors and finally grouping available gas sensors into a clustered system. The first task of WP4 included a review of the state of the art of gas sensors. The review considered NO2 graphene sensors and commercially available micro-sensors including solid state sensors, electrochemical sensors and miniaturised spectroscopic sensors for NO/NO2/NOx, O3, SO2, CO and benzene.The second task consisted in the production of two graphene sensors with enhanced sensitivity on both exfoliated graphene and epitaxial graphene.In the third task of the project, currently on-going, a protocol for the evaluation of gas sensor is developed and testing of performances of NO2 and O3 sensors is carried out. Based on the review, the graphene sensors and a set of commercial sensor were selected. Tests took place in laboratory in exposure chamber and at one field site. A large automated exposure chamber specialized for gas sensor test was developed.The aim of the final task of WP4, that will take place next year, is to cluster single sensors to a performing system able to detect NO/NO2/NOx, CO, SO2, O3 and benzene, the gaseous compounds that are regulated in the European air quality Directive. The protocol for evaluating sensors has been developed. It involves detecting significant parameters of the sensors (e.g. response time, drift, hysteresis, gaseous/physical/meteorological interference…) that are used to establish an empirical model describing sensors responses. Subsequently, the suitability of the model is tested under field conditions. This protocol was applied to 11 models of O3 sensors. It is now applied to 7 models of NO2 sensors. Data treatment is going-on in order to prepare evaluation reports for all sensors.