On June 22, 2026, air quality in Basel was notably elevated due to high ozone concentrations. The maximum ozone level reached 160.7 µg/m³, which ranks as the 4th highest daily maximum in the past 365 days. This value exceeded the regulatory threshold of 120 µg/m³, triggering an exceedance. The average ozone concentration for the day was 103.4 µg/m³, which is significantly above the 30-day average of 77.7 µg/m³ and the seasonal average of 71.4 µg/m³. This indicates a substantial spike in ozone levels compared to recent and seasonal norms.

Nitrogen dioxide and PM10 levels remained within regulatory limits. The maximum NO₂ concentration was 20.8 µg/m³, well below the 80 µg/m³ daily average standard, and its average of 9.6 µg/m³ was slightly above the 30-day average of 6.0 µg/m³. The maximum PM10 concentration was 28.1 µg/m³, and its average of 22.1 µg/m³ was above the 30-day average of 15.4 µg/m³ but still below the 50 µg/m³ daily average standard.

Compared to historical data since 2018, the maximum ozone concentration of 160.7 µg/m³ is below the all-time maximum of 206.3 µg/m³ recorded on June 27, 2019. The current value ranks 34th highest all-time, indicating it is high but not unprecedented. The maximum NO₂ and PM10 concentrations on this day were far below their historical maxima of 83.2 µg/m³ and 165.1 µg/m³, respectively.

Overall, the air quality on June 22, 2026, was unusual due to the notably elevated ozone levels. The high ozone concentration, ranking 4th in the past year and exceeding the regulatory threshold, is the primary concern. This elevation is likely driven by strong solar radiation and high temperatures typical of summer, which promote photochemical ozone formation. While NO₂ and PM10 were within normal ranges, the ozone exceedance indicates a significant air quality event that warrants attention, particularly for sensitive groups.