On August 8, 2026, air quality in Basel was notably impacted by elevated ozone levels. The maximum ozone concentration reached 150.8 µg/m³, which exceeded the regulatory threshold of 120 µg/m³ for the maximum hourly average. This value ranked as the 18th highest daily maximum in the past 365 days. In contrast, nitrogen dioxide and particulate matter remained well within typical bounds. The maximum nitrogen dioxide was 11.6 µg/m³ and the average was 7.8 µg/m³, both far below the daily average standard of 80 µg/m³. For PM10, the maximum was 16.2 µg/m³ and the average was 13.1 µg/m³, also comfortably under the 50 µg/m³ daily average limit.

Comparing the day’s measurements to historical data since 2018, the ozone maximum of 150.8 µg/m³ was above the seasonal average maximum of 175.8 µg/m³ but below the all-time record of 206.3 µg/m³ set on June 27, 2019. The day’s average ozone of 110.9 µg/m³ was higher than both the 30-day average of 99.3 µg/m³ and the seasonal average of 88.7 µg/m³, indicating a period of sustained elevated ozone. Nitrogen dioxide and PM10 values were unremarkable historically; the NO2 maximum ranked 2,655th out of 2,987 days, and the PM10 maximum ranked 1,712th, placing them firmly in the lower range of all observations.

Overall, the air quality on this day was characterized by a significant ozone event, while other pollutants remained at low, historically consistent levels. The elevated ozone is consistent with summertime photochemical smog conditions, where intense sunlight and precursor pollutants drive ozone formation. The exceedance of the 120 µg/m³ threshold underscores the potential for respiratory irritation and the importance of monitoring during hot, sunny periods.