Ozone exceeds Swiss limit while PM10 spikes near threshold
July 26, 2026On July 25, 2026, Basel experienced elevated air pollution with ozone exceeding the Swiss hourly limit of 120 µg/m³ and fine particles (PM10) peaking just below the daily average limit, marking one of the highest PM10 levels in the past year. The simultaneous elevation of both pollutants was unusual, with the PM10 spike being particularly exceptional relative to recent history.
On July 25, 2026, air quality in Basel was classified as considerable (KBI rating 15–19), reflecting elevated levels of ozone and a pronounced spike in fine particles. Ozone reached a maximum hourly concentration of 147.2 µg/m³, exceeding the Swiss regulatory threshold of 120 µg/m³ that may be surpassed only once per year. Fine particles (PM10) peaked at 49.1 µg/m³, just below the daily average limit of 50 µg/m³, but this maximum was among the highest observed in the past twelve months. Nitrogen dioxide remained unremarkable, with a daily average of 7.4 µg/m³ and a maximum of 12.6 µg/m³, both well below the 80 µg/m³ daily average standard.
The daily average ozone concentration was 107.0 µg/m³, while the PM10 average stood at 14.4 µg/m³. The PM10 maximum of 49.1 µg/m³ matched the highest value recorded so far this season and was the 12th highest daily maximum in the last 362 days. By contrast, the ozone maximum ranked 18th over the same period, placing it within the top five percent of daily peaks. No regulatory threshold was exceeded for nitrogen dioxide or for the daily average of PM10.
Compared to historical data since 2018, the ozone levels were above the seasonal average of 85.9 µg/m³ and the 30-day average of 95.4 µg/m³, though the maximum remained well below the all-time record of 206.3 µg/m³ set on June 27, 2019. Nitrogen dioxide values were close to long-term norms, with a maximum far below the historical peak of 83.2 µg/m³. The PM10 average was slightly above seasonal norms, and the daily maximum tied the highest value seen in the current season, but it remained far below the absolute record of 165.1 µg/m³ from August 24, 2023.
Overall, the day exhibited a mixed air quality pattern, with ozone reaching summertime exceedance levels and PM10 briefly approaching its regulatory ceiling. The high ozone is typical of photochemical pollution during warm, sunny conditions, while the PM10 spike likely reflects a short-lived episode, possibly from local dust or a transport event. The combination was unusual in that both pollutants were simultaneously elevated, though the more exceptional signal was the PM10 maximum relative to recent history.
Table 1: Statistics for Air Quality Parameters on 2026-07-25
| Constituent | Average µg/m³ | Maximum µg/m³ | Standard | Comments |
|---|---|---|---|---|
| NO2 | 7.7 | 26.4 | 80.0 | daily average may not exceed standard |
| Ozone | 94.5 | 175.3 | 120.0 | maximum hourly average may exceed standard only one time per year |
| PM10 | 12.7 | 49.1 | 50.0 | daily average may not exceed standard |
Table 2: Statistics for Air Quality Parameters for the Month of July, since 2018
| Constituent | Average µg/m³ | Max µg/m³ | Exceedances |
|---|---|---|---|
| NO2 | 7.8 | 56.2 | 0 |
| Ozone | 77.5 | 181.9 | 103 |
| PM10 | 11.5 | 49.1 | 0 |
Figure 1: NO2 Concentrations in Basel, last 90 Days
Figure 2: Ozone Concentrations in Basel in the last 90 Days
Figure 3: PM10 Concentrations of last 90 Days at Binningen/Basel
Additional resources: Umweltbericht beider Basel, Luftqualität Nordwestschweiz, Luftreinhalte-Verordnung (LRV)
🤖 This text was generated with the assistance of AI. All quantitative statements are derived directly from the dataset listed under Data Source.