In 2024, the environment ministries of EU Member States adopted the revised Ambient Air Quality Directive (AAQD 2024) – a landmark update that raises the bar for how Europe measures, manages, and communicates air pollution. The directive introduces stricter limit values, strengthens the role of indicative measurements, and places greater responsibility on local and regional authorities to demonstrate that their decisions are grounded in reliable evidence.

Member States now have the time until December 2026 to transpose the directive into national law, with full implementation required by 2030. The timeline establishes clear expectations regarding air quality improvements, data robustness, and transparency in monitoring practices.

Air quality is no longer a peripheral environmental topic. It is a compliance challenge, a public‑health priority, and increasingly a political pressure point. The question facing cities, regions, and regulated industries is no longer whether to measure air quality – but how to measure it in a way that is defensible, precise, and aligned with the new regulatory landscape.

The 2024 AAQD establishes indicative measurements as a central, legitimate, and strategically significant component of Europe’s air quality system, functioning as a complement to fixed reference stations.

What the New Directive Requires

The revised AAQD introduces several major shifts:

• stricter limit values for key pollutants, including PM2.5 and NO₂
• higher expectations for spatial coverage, especially in urban areas
• greater transparency and public access to data
• clearer obligations for local authorities to justify decisions with evidence
• formal recognition of indicative measurements as part of compliance strategies.

The European Commission has already initiated work on new EN standards for evaluating sensor systems for gaseous pollutants and particulate matter (PM10 and PM2.5). Until these standards are completed, the directive allows the use of CEN Technical Specifications in place of harmonised EN methods.

This closes a long‑standing gap. For years, Europe lacked a common “yardstick” for assessing the reliability of sensor‑based measurements. The AAQD now provides the framework to change that.

What the Directive Enables: From Compliance to Capability

By elevating the role of indicative measurements, the AAQD unlocks new possibilities for cities, regions, and regulated sectors:

• Better spatial coverage: Reference stations are accurate but sparse. Indicative measurements allow authorities to fill the gaps – street by street, neighbourhood by neighbourhood.
• More responsive decision‑making: With continuous, distributed data, authorities can track pollution peaks in real time and respond proactively rather than reactively.
• Stronger evidence for policy: Whether designing Clean Air Zones, adjusting traffic flows, or planning new infrastructure, high‑resolution data makes decisions more defensible.
• Improved public communication: Transparent, localised data builds trust and reduces resistance to interventions.
• Operational intelligence for industry: Mining, chemical, and manufacturing sites can monitor dispersion patterns, verify mitigation measures, and demonstrate compliance.

In short, indicative measurements turn air quality monitoring into a strategic asset rather than a compliance checkbox.

TS 17660: Ending the “Grey Zone” of Sensor Quality

One of the most important developments accompanying the AAQD is the emergence of CEN Technical Specification TS 17660, which finally provides a structured, Europe‑wide framework for evaluating sensor performance.

For years, the sensor market operated in a “grey zone”: many devices claimed accuracy, but there was no unified method to verify those claims. TS 17660 changes that.

TS 17660 does not prescribe how sensors must be constructed; instead, it sets out how they should be tested and what performance they are expected to achieve. It also introduces performance classes – analogous to energy‑efficiency labels for household appliances – to enable transparent comparison between devices by authorities.

The specification is divided into two parts: Part 1 covers gaseous pollutants such as NO₂, O₃, and CO, while Part 2 addresses particulate matter, specifically PM2.5 and PM10.

By providing a shared European reference framework for evaluating sensor‑based air quality systems, it ensures that all devices are assessed against consistent criteria.

By doing so, it supports fair competition among manufacturers, who must demonstrate performance under comparable conditions rather than relying on unverified claims. The specification also strengthens the position of authorities, giving them confidence that indicative measurements produced by compliant systems meet a recognised and credible standard.

As a result, it helps shift the market away from low‑cost, untested devices toward solutions that are independently assessed, certified, and ultimately more trustworthy for regulatory and public‑health purposes.

In the coming years, certified performance will matter more than low price – a shift that ultimately benefits public authorities and residents.

A Challenge or a Transformative Opportunity?

The 2024 AAQD raises expectations, but it also provides the tools needed to meet them. Indicative measurements, supported by TS 17660, give cities and regulated sectors the clarity they need to act confidently. For local authorities, this translates into stronger evidence for planning and policy, more defensible decisions, earlier identification of emerging risks, greater public trust, and a more predictable path toward 2030 compliance.

For the industry, the new framework enables transparent monitoring practices, real‑time operational insights, and more constructive relationships with regulators and surrounding communities.

Meeting these expectations will require investment, planning, and adaptation, but the result is a monitoring ecosystem that is more precise, more transparent, and better aligned with Europe’s long‑term environmental objectives.

As Europe moves toward stricter standards and greater accountability, indicative measurements are no longer optional – they are essential. With well-designed networks, they can empower organisations to move from reactive compliance to proactive environmental stewardship.

If your organisation is exploring how to align with the AAQD or how to build a monitoring network that meets future requirements, Airly’s team is always ready to support you.