---
title: Classes based on CEN/TS 17660
description: 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.
---

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1. [Regulations and standards](https://support.airly.org/airly/regulations-and-standards)

# 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**](https://www.csagroup.org/en-gb/services/mcerts/mcerts-product-certification/mcerts-certified-products/mcerts-certified-products-low-cost-air-quality-sensor-systems-part1-gaseous-pollutants-in-ambient-air/) use this standard for certifying low-cost air quality monitors.

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