The report Traffic and urban air quality in the Spanish State, published by Ecologists in Action, analyzes the location of air quality monitoring stations oriented to traffic in 25 Spanish cities, including the country's main urban agglomerations. Over the last decades, they point out in the study, many regional and local administrations have relocated stations considered “problematic”, especially traffic ones, towards secondary roads.
This practice, according to the analysis, has been justified by compliance with legal criteria, “but it has resulted in preventing the highest levels of pollution from appearing reflected in official records, thus reducing their public visibility,” they warn.
The European legal framework tightens the rules
The debate about the location of these stations is not exclusive to Spain. As recalled by Ecologistas en Acción, this problem led to a relevant judgment by the Court of Justice of the European Union in 2019, in relation to the city of Brussels.
This precedent has directly influenced the development of the new Directive 2024/2881 on ambient air quality, currently in the process of transposition in Spain, which introduces stricter criteria on where measurement points should be located.
The regulation establishes that stations intended to protect human health must be located at points that reliably reflect pollution levels, especially in sensitive areas such as residential areas, educational centers, hospitals or office spaces.
The Directive also sets specific conditions when the objective is to measure pollution derived from road traffic. In these cases, sampling points must be located in streets where the highest concentrations of pollutants are recorded.
For this, factors such as traffic density, dispersion conditions, and urban configuration must be taken into account, including spaces such as the so-called “urban canyons”.
Furthermore, European regulations require that each zone has at least one station located at a critical pollution point to measure substances such as nitrogen dioxide (NO₂), suspended particles (PM10 and PM2.5), benzene or carbon monoxide (CO). In cases where there is only one measurement point, this must be obligatorily located in a critical zone.
Results: widespread non-compliance
In light of these criteria, the report by Ecologistas en Acción concludes that 19 of the 25 stations analyzed—that is, three out of every four—present some type of limitation in their location, either due to partial or complete non-compliance.
In six agglomerations —Barcelona, Bilbao, Elche, Granada, Santander and Valladolid— the traffic stations are not located on the streets with the highest concentration of pollution, which implies that they do not comply with the definition of critical point established by European regulations.
In addition, cities like Badajoz, Guadalajara and Logroño directly lack traffic stations, since the only existing ones are located in background areas, far from the main emission sources.
Technical deficiencies in the location of the stations
The report also identifies problems in the so-called micro-implantation, that is to say, in the immediate conditions of the environment where the meters are located.
Among the most relevant deficiencies, Ecologistas en Acción points out excessive sampling heights in cities like Bilbao and Las Palmas de Gran Canaria, as well as distances greater than 10 meters from the edge of the roadway in multiple locations, including A Coruña, Alicante, Madrid, Málaga or San Sebastián.
These factors, according to the analysis, can alter the representativeness of the collected data, affecting their technical validity and their comparability, in a context in which the new European regulation demands greater precision and rigor in the measurement of air quality.