Classes based on CEN/TS 17660

The CEN/TS 17660 standard classifies air quality sensor systems into three performance classes (Class 1, Class 2, and Class 3) based on their accuracy, reliability, and data quality objectives.

The classification provides a harmonized protocol for evaluating sensor performance through laboratory and field tests. The resulting classes are:

• Class 1: These sensors offer the highest accuracy and reliability. They are suitable for "indicative measurements" and "objective estimation" as defined in the European Air Quality Directive (2008/50/EC) and often provide data quality close to traditional reference standards.
• Class 2: These sensors have more flexible performance criteria than Class 1 and are generally used for non-regulatory applications where less stringent data quality is acceptable.
• Class 3: These sensors have the broadest performance range and are typically used for applications requiring less rigorous data quality, such as general information or awareness campaigns.

The specific class a sensor achieves depends on factors like its coefficient of variation (inter-sensor variability) and the number of sensor systems used in testing. Certification bodies like MCERTS use this standard for certifying low-cost air quality monitors.