Why Air Quality Standards Matter: Building Trust Through Regulatory Frameworks

For local authorities, making effective air quality decisions depends on one thing above all: reliable data. That means data that is not only accurate and consistent but also aligned with recognised regulatory guidance. Without these frameworks in place, even the most innovative sensor networks risk delivering insights that lack credibility—making it difficult to inform policy, assess compliance, or safeguard public health. Regulatory guidance helps ensure that emerging technologies—like low-cost air quality sensors—can meet the expectations of legislation, enabling confident, long-term decision-making.

CEN/TS 17660-1: Setting the Benchmark for Sensor Accuracy

CEN/TS 17660-1:2021 establishes a harmonised testing methodology for evaluating the performance of air quality sensor systems that monitor gaseous pollutants in ambient air. Critically, it links sensor classification to the data quality objectives (DQOs) defined in European Directive 2008/50/EC. ( Replaced recently by Directive (EU) 2024/2881 )

Under this standard, sensors are assessed and categorised into three performance classes:

• Class 1 – suitable for indicative measurements 

• Class 2 – suitable for objective estimations 

• Class 3 – suitable for non-regulatory or informal monitoring applications 

The testing process includes laboratory evaluation, environmental simulations, and field deployments to assess parameters such as response time, drift, repeatability, cross-sensitivity, and overall measurement uncertainty.

In the UK, the Environment Agency's MCERTS scheme is expected to adopt this standard for gaseous sensors. EarthSense intends to submit its Zephyr® sensor for formal testing, with the goal of achieving Class 1 certification—making it a premium choice for local authorities that require robust, regulation-ready indicative data.

PAS 4023: Practical Deployment Guidance for the UK

While CEN/TS 17660-1 focuses on how sensors are evaluated, PAS 4023 provides a practical framework for deploying and managing low-cost air quality sensors in real-world environments. Developed with support from Defra, and in collaboration with the National Physical Laboratory, EarthSense, leading environmental consultants, sensor manufacturers and several UK local authorities, PAS 4023 offers non-mandatory but regulator-supported guidance for public bodies using sensor networks.

Key highlights of PAS 4023 include:

• Guidance on choosing the right sensor system based on pollutant targets, site-specific challenges, and measurement purpose.

• Best practices for deployment—including optimal siting, avoidance of local interference (e.g. walls or vegetation), and access to power and airflow 

• Recommendations for ongoing calibration and maintenance, including co-location with reference monitors.

• A focus on data transparency through robust documentation.

For local authority air quality officers, public health teams, and environmental practitioners, PAS 4023 provides a trusted roadmap for building high-quality, actionable sensor data programs—even where formal compliance monitoring isn't the goal.

Why This Matters

Together, CEN/TS 17660-1 and PAS 4023 give local authorities the tools they need to expand monitoring networks confidently and responsibly. As the UK continues to integrate sensor technology into policy, planning, and public engagement, aligning with these frameworks ensures the data you rely on is not just available—but credible and defensible.

At EarthSense, we’re committed to helping local authorities meet these expectations. With Network QAQC and upcoming Zephyr certification, we’re proud to support communities in creating cleaner, healthier environments with data they can trust.