On July 15, 2026, air quality in Basel was characterized by elevated ozone concentrations. The maximum ozone level of 175.3 µg/m³ was the second highest recorded in the past 365 days. This value exceeded the regulatory threshold of 120 µg/m³, which is the maximum hourly average allowed under the Luftreinhalte-Verordnung. The average ozone concentration for the day was 112.8 µg/m³.

The maximum ozone level was also notably high compared to historical data since 2018, ranking 12th out of 2963 days. The all-time maximum ozone concentration in Basel was 206.3 µg/m³, recorded on June 27, 2019. The average ozone concentration on July 15 was above the 30-day average of 93.0 µg/m³ and the seasonal average of 83.6 µg/m³.

Nitrogen dioxide and PM10 levels remained within regulatory limits. The maximum NO₂ concentration was 23.5 µg/m³, well below the daily average limit of 80 µg/m³. The average NO₂ concentration was 12.6 µg/m³, which is higher than the 30-day average of 7.9 µg/m³ and the seasonal average of 6.7 µg/m³. The maximum PM10 concentration was 35.8 µg/m³, and the average was 23.3 µg/m³, both below the daily average limit of 50 µg/m³. The average PM10 concentration was above the 30-day average of 16.4 µg/m³ and the seasonal average of 13.6 µg/m³.

Overall, the air quality on July 15, 2026, was unusual due to the significantly elevated ozone levels. The high ozone concentration is characteristic of strong photochemical activity, which typically occurs during periods of high temperature and intense sunlight. The elevated NO₂ and PM10 averages, while still within limits, suggest increased local emissions, likely from traffic or other combustion sources, which contributed to the formation of ozone.