Ozone alone drives considerable air quality rating in Basel
September 9, 2026On 2026-09-08, ozone was the only pollutant to exceed its Swiss regulatory limit, reaching a maximum hourly concentration of 136.5 µg/m³ and driving an overall “considerable” air quality rating, while nitrogen dioxide and PM10 remained unremarkable. The ozone exceedance was elevated relative to the season but not historically extreme, ranking in the top 7 percent of daily maxima since 2018 and consistent with occasional warm-weather ozone events in Basel.
On 2026-09-08, ozone was the only pollutant to exceed its regulatory threshold. The maximum hourly ozone concentration reached 136.5 µg/m³, above the Swiss limit of 120 µg/m³, while the daily average was 84.1 µg/m³. Nitrogen dioxide and PM10 remained well below their respective limits, with maximum values of 24.6 µg/m³ and 29.1 µg/m³, and daily averages of 11.0 µg/m³ and 23.0 µg/m³. The overall air quality rating was “considerable,” driven entirely by the ozone exceedance.
Compared with the past 365 days, the maximum ozone value ranked 38th out of 362 days, placing it in the upper tenth but not among the most extreme recent events. The maximum NO2 value ranked 176th, and the maximum PM10 value ranked 59th, both unremarkable. Over the last 30 days, the average ozone mean was 79.7 µg/m³, and there had been one previous exceedance, so the current exceedance is not unprecedented for this period. For the season to date, the average ozone mean was 69.0 µg/m³, and no exceedances had occurred before this day, making the current event the first seasonal exceedance.
Historical data since 2018 show that the all-time maximum ozone concentration was 206.3 µg/m³ on 2019-06-27. The current maximum of 136.5 µg/m³ ranks 207th out of 3018 days, placing it in the top 7 percent of all daily maxima but far below the record. The all-time maximum NO2 was 83.2 µg/m³ on 2019-02-15, and the current maximum of 24.6 µg/m³ ranks 1660th, indicating a typical low value. The all-time maximum PM10 was 580.2 µg/m³ on 2026-08-15, only about three weeks earlier, and the current maximum of 29.1 µg/m³ ranks 506th, suggesting a return to more normal PM10 levels after that extreme event.
Overall, air quality on 2026-09-08 was dominated by a moderate ozone exceedance. This is consistent with warm, sunny late-summer conditions that promote photochemical ozone formation. The ozone level was elevated relative to the season but not historically extreme. NO2 and PM10 were unremarkable. The day’s air quality was therefore unusual only for ozone, and the exceedance, while notable, falls within the range of occasional summer ozone events seen in Basel since 2018.
Table 1: Statistics for Air Quality Parameters on 2026-09-08
| Constituent | Average µg/m³ | Maximum µg/m³ | Standard | Comments |
|---|---|---|---|---|
| NO2 | 8.4 | 29.3 | 80.0 | daily average may not exceed standard |
| Ozone | 69.0 | 136.5 | 120.0 | maximum hourly average may exceed standard only one time per year |
| PM10 | 10.0 | 29.1 | 50.0 | daily average may not exceed standard |
Table 2: Statistics for Air Quality Parameters for the Month of September, since 2018
| Constituent | Average µg/m³ | Max µg/m³ | Exceedances |
|---|---|---|---|
| NO2 | 10.9 | 55.5 | 0 |
| Ozone | 56.4 | 156.1 | 37 |
| PM10 | 10.5 | 42.0 | 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.