Air quality in Brussels has not improved between 2023 and 2025. This is evident from measurements taken by the BRAL urban movement, with support from Brussels Environment, as part of the ExpAIR campaign.
What’s more, annual nitrogen dioxide concentrations even rose slightly at the 24 measuring stations. According to BRAL’s ExpAIR report, this result is partly attributable to the postponement of stricter Low-Emission Zone (LEZ) rules.
Stagnation in improvement
At three of the 24 measurement locations – ‘black spots’ according to BRAL, where there are no official measuring stations – the current European limit value of 40 µg/m³ was exceeded.
These illegal values were measured at Toison D’Or/De Guldenvlieslaan (48.58 µg/m³), Porte de Flandre/De Vlaamsepoort (44.14 µg/m³), and Rue Piers/De Piersstraat in Molenbeek (45.15 µg/m³). In addition, all 24 measuring points exceed the new European limit value of 20 µg/m³ that will come into force in 2030.
The figures also confirm the trend that the NO2 average is stagnating and even rising slightly. During the measurement period covered by the report (June ’24 – June ’25), the average of the 24 measuring points was 33.2 µg/m³. In previous measurements during 2023-2024, the average was 32.4 µg/m³.
Due to the postponement of the LEZ tightening
According to BRAL, the stagnating figures can be attributed to the postponement of the LEZ tightening. “Look at CurieuzenAir,” says BRAL.
CurieuzenAir, the largest citizen-led air quality study ever conducted in Brussels, found that air quality improved significantly between 2019 and 2021. In most places, nitrogen dioxide concentrations fell by an average of 10% to 15% compared to official measurements in 2019 – the LEZ was introduced in the Brussels-Capital Region in 2018.
However, now that there is talk of a postponement again, those gains in the ExpAIR figures are evaporating, says BRAL, a claim confirmed by the official evaluation of the LEZ, which found that the decline in the share of diesel cars in Brussels suddenly levelled off in mid-2024.
“This slowdown in the trend can be attributed to the announcement of the postponement of the August 2024 milestone. This illustrates the impact of the LEZ on the composition of the vehicle fleet,” states the report.
Lost year
BRAL therefore argues that the figures show that postponing the planned LEZ phase of 2025 means a lost year for improving air quality in Brussels. Since the announcement of the LEZ phase’s postponement, which was supposed to start on January 1, 2025, the number of polluting Euro 5 diesel cars in Brussels has not decreased further.
“The effectiveness of the LEZ depends on a clear roadmap and timetable, which gives citizens the necessary insight and time to adapt their behavior,” says Lauren de Crombrugghe of BRAL. “The recent political uncertainty leaves no room for this and only creates more confusion.”
For your information: The new phase of the LEZ officially came into effect on January 1, 2026. This ban was originally postponed by parliament until 2027, but the Constitutional Court overturned that postponement at the end of 2025.
Although the ban has been in force since January, a transition period has been established. Anyone driving a prohibited vehicle will currently only receive a warning in the mail. From April 1, 2026, the warnings will stop, and effective fines will be issued.
A fine currently amounts to €350. You can receive a maximum of one fine per quarter. However, a proposal on the table would reduce the fines to €80 or €150 and introduce an annual pass that would allow people to enter the city with their old cars for a fee.
More space for cyclists and pedestrians
BRAL also emphasizes that one in six Brussels residents suffers from a respiratory condition. “That is why policy must continue to focus on health.” It also wants more space for cyclists and pedestrians to reduce road traffic emissions directly. Seventy percent of public space in Brussels is reserved for cars.
