Pollution Episodes
Details of major pollution episodes including peak values recorded across
Ealing Council.
Please select an episode to view from the list below:
First High Ozone Episode of 2026
Thursday, 13th August 2026
With the continuation of extreme summer weather, London experienced its first 'High' Ozone episode of 2026 yesterday, Thursday, 13th August. While 'Moderate' readings had been consistently recorded over recent days, the episode intensified significantly yesterday, peaking with four monitoring sites across the capital reaching 'High' levels.
Elevated concentrations were driven by a combination of local environmental conditions and transboundary pollution. Strong sunshine and extreme heat acted as the primary catalysts for photochemical reactions, heavily fuelling the production of ground level ozone from both local and continental precursor emissions.
Notably, a substantial early day influx of Nitrate and Ammonia drove these elevated concentrations, triggering a much earlier peak than we have observed in recent days. This sudden import occurred because the incoming air mass briefly looped over mainland Europe before reaching London, sweeping up a secondary stream of precursor pollutants along its path. Interestingly, this event is somewhat of an anomaly, we have not recorded any significant pollution accumulation of this type from this specific trajectory so far this year.
This process was further intensified by atmospheric stability. Light breezes resulted in poor dispersion of local emissions, allowing them to accumulate and react with the imported continental pollutants with much greater intensity.
The National Daily Air Quality Index (DAQI) for Ozone is calculated based on a running 8-hour mean. It is important to note that ozone is an area-wide pollutant. Although monitoring sites are sparse, they represent wider population exposure. A 'High' reading at a single site strongly indicates that hundreds of thousands of people across the surrounding area have been exposed to similar concentrations.
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