High Fens smoke drove extreme air pollution while Walloon alert rules stayed inactive

Updated 24 August 2026 — Smoke from the High Fens wildfire drove the PM2.5 concentration in Vielsalm to almost 700 micrograms per cubic metre at 11:00 on Sunday, 16 August, according to the Belgian Interregional Environment Agency, IRCEL-CELINE. The agency said concentrations had returned to seasonally normal levels at its permanent Walloon monitoring stations by Wednesday, although pollution remained possible near the fire.

The Vielsalm reading was a short-lived local peak, not a 24-hour average. IRCEL-CELINE also measured peaks of 230 micrograms per cubic metre at Sinsin and 210 at Dourbes. For comparison, the agency cites a World Health Organization guideline of 15 micrograms per cubic metre for PM2.5 averaged over 24 hours. It reported elevated fine particles and black carbon across much of Wallonia from midday on Sunday as changing winds carried smoke tens of kilometres from the burning plateau.

RTBF reported that the population was poorly informed about the severity of the pollution while the smoke was passing. IRCEL-CELINE’s subsequent explanation said the episode remained too limited in duration and geographical extent to activate Wallonia’s formal information threshold, which uses a regional 24-hour PM2.5 average of 35 micrograms per cubic metre. The existing system is designed around sustained, widespread smog episodes rather than rapidly moving wildfire plumes.

Walloon authorities later published precautions supplied by the regional health agency AVIQ. The guidance advised people exposed to smoke to remain indoors, close windows and doors, stop mechanical ventilation, avoid strenuous outdoor activity and use an FFP2 mask when going outside. It identified people with respiratory or cardiovascular conditions, older residents, young children and pregnant women as requiring particular vigilance.

Monitoring has since expanded. ISSeP said seven additional micro-sensors were deployed from 17 August around the affected area, while mobile reference stations were installed at schools in Eupen and Jalhay on 20 August. Laboratory work is also examining pollutants including polycyclic aromatic hydrocarbons.

The immediate pollution spike has passed at permanent stations, but the communication failure remains unresolved. Authorities have not announced whether Wallonia will add a faster warning mechanism for intense local smoke events. Results from ISSeP’s supplementary sampling and any official review of the alert response are the next findings to watch.