Air Affair – On air quality in Brussels
Context and background
BRAL has been working for years to improve air quality in Brussels, combining scientific measurements with citizen‑science projects such as CurieuzenAir and ExpAIR. These earlier initiatives revealed persistent problem areas, and highlighted the need for long‑term monitoring and a better understanding of how pollution affects daily life. With The Air Affair, BRAL continues this work by expanding the secondary NO₂ measurement network and strengthening a community of organisations and ambassadors committed to cleaner air across the city.
Continues below the map: NO₂ concentration in Brussels.
© CurieuzenAir 2021
What were the objectives of this project?
BRAL aimed for a CDK deployment and online survey to complement the technical measurements by capturing how people actually perceive air quality in the places where they live, work and travel. The goal was to reach residents directly in highly polluted, high‑traffic locations, lower the participation barriers through both physical and digital access, and gather a large, diverse set of opinions that would help BRAL understand the lived experience behind the data and support future policy and community action.
Continues below the picture: Location “Vlaamsepoort-Porte de Flandre”.
How was this implemented?
During March 2026, 4 Dialog Boxes were installed at Zwarte Vijvers, the Vlaamsepoort, the Gulden‑Vlieslaan and U‑Square, all chosen for their combination of poor air quality and heavy foot traffic. The survey was also available online, allowing anyone in Brussels to participate. Together, these channels generated 1.496 interactions, including 829 fully completed surveys, giving BRAL a substantial dataset to analyse. The deployment also activated a network of local ambassadors who helped communicate the project and will later share the results within their neighbourhoods.
The questions were presented in three languages (Dutch, French and English) to accommodate the diversity of visitors.
Continues below the chart: Survey engagement per day, per location.
Engagement overview
When looking at the participation flow across the four locations, each site showed its own rhythm. Zwarte Vijvers and the Vlaamsepoort followed the classic pattern we often see in dense urban areas, with regular fluctuations and a drop‑off over time. Porte de Namur behaved differently: engagement remained remarkably constant throughout the entire deployment, suggesting that the steady foot traffic in this area kept participation high day after day. Etterbeek stood out as well, with a clear uptick in interactions toward the end of the deployment. We believe it was due to a local event happening near the end of the deployment.
In total, 1,496 people started the survey and 829 completed it, resulting in a 55% completion rate. This is significantly higher than expected for a public‑space deployment with a questionnaire of 16-18 questions, where completion rates often hover around 40% or even lower. The strong performance shows that participants were willing to stay engaged despite the length, and the average number of questions answered remained consistent with what we typically observe in similar projects.
Language distribution also revealed a clear pattern. Across all channels, French was the most common starting language with 863 participants (57.6%), followed by Dutch with 260 participants (17.4%) and English with 253 participants (16.9%). A smaller group, 122 participants (8.1%), selected “No opinion.”
Continues below the picture: Location “Naamsepoort-Porte de Namur”.
What were the insights from the deployment?
How residents feel about air pollution
The survey shows that air pollution is a concrete concern for many people in Brussels. Almost half of all respondents say they are affected by polluted air in some way, which can range from unpleasant smells to respiratory symptoms. 67% say they do not feel well informed about air quality or its health effects. At the same time, concern is high: 84% describe themselves as somewhat or very worried about pollution in the city. Health is the main reason for this concern. 32% say they experience discomfort linked to air pollution during certain activities, 13% report having a respiratory condition and 17% know someone who has one. Only 38% say they notice no effects at all.
Continues below the charts.
Perceptions of air quality & its causes
Perceptions of how air quality has evolved are mixed. Forty three percent believe the situation has worsened in recent years, even though official NO₂ measurements show a decline between 2021 and 2024 followed by stagnation. The survey also highlights that NO₂ is only one part of the picture. Fine particles, emissions from heating and wood burning all contribute to the overall burden. Wood burning alone accounted for 17% of fine particle pollution in Brussels in 2023. When respondents were shown the measured NO₂ levels at the survey locations, 59% said they were not surprised, often because they expect higher pollution in busy areas. At the same time, 60% disagree with the idea that pollution is simply unavoidable in cities. 83% consider the current levels unacceptable or completely unacceptable.
Continues below the charts.
Expectations for policy and future action regarding air quality
There is also strong support for more ambitious action. Half of the respondents say they are willing to change their own behaviour to improve air quality, and only 3.5% would do so only if stricter rules were imposed. 70% support aligning Brussels’ policies with the WHO guidelines, and 83% say that any measures must remain socially fair. Satisfaction with current efforts is low, with only 9% saying they are satisfied. When asked who should take the lead, most point to the Brussels Region, followed by the federal government and the European Union. Road traffic is seen as the top priority for future measures, followed by industry, while heating systems are mentioned less often despite their role in particulate pollution. Overall, the results show a clear demand for better information, stronger political commitment and continued research into how residents experience the health effects of polluted air.
Continues below the charts.
Reflections on The Air Affair
Combining quantitative results gathered with air quality sensors and qualitative input collected through Citizen Dialog Kit gave BRAL a fuller view of how people engaged with the project. The four locations showed different interaction progressions, which allowed for interesting insights and showed how people interact with public space differently.
The completion rate was unusually high for a long survey (16-18 questions) in a busy environment, which suggests that people were willing to stay with it. Offering the survey in three languages mattered in a city like Brussels and shaped who participated at each site.
The survey also revealed things that sensors cannot show. Many respondents felt air quality had worsened, even though the measurements tell a another story. This gap between perception and data is important for communication and policy. Taken together, the measurements and Citizen Dialog Kit created a more complete picture of air quality in Brussels. The data showed what is happening, and the survey helped explain how people interpret it and what they expect from authorities.
