Can commercial low-cost sensor platforms contribute to air quality monitoring and exposure estimates?

The emergence of low-cost, user-friendly and very compact air pollution platforms enable observations at highspatial resolution in near-real-time and provide new opportunities to simultaneously enhance existing monitor-ing systems, as well as engage citizens in active environmental monitoring. This provides a whole new set of ca-pabilities in the assessment of human exposure to air pollution. However, the data generated by these platformsare often of questionable quality.We have conducted an exhaustive evaluation of 24 identical units of a commercial low-cost sensor platformagainst CEN (European Standardization Organization) reference analyzers, evaluating their measurement capa-bility over time and a range of environmental conditions. Our results show that their performance varies spatiallyand temporally, as it depends on the atmospheric composition and the meteorological conditions. Our resultsshow that the performance varies from unit to unit, which makes it necessary to examine the data quality ofeach node before its use.In general, guidance is lacking on how to test such sensor nodes and ensure adequate performance prior to mar-keting these platforms. We have implemented and tested diverse metrics in order to assess if the sensor can beemployed for applications that require high accuracy (i.e., to meet the Data Quality Objectives defined in air qual-ity legislation, epidemiological studies) or lower accuracy (i.e., to represent the pollution level on a coarse scale,for purposes such as awareness raising).Data quality is a pertinent concern, especially in citizen science applications, where citizens are collecting andinterpreting the data.In general, whilelow-costplatforms present low accuracy for regulatory orhealth purposesthey can provide relative and aggregated information about the observed air quality