On August 3, 2026, the air quality in Basel was notably influenced by elevated ozone levels. The maximum ozone concentration reached 148.9 µg/m³, which ranked as the 20th highest daily maximum in the past 365 days. This value exceeded the regulatory threshold of 120 µg/m³ for the maximum hourly average, triggering an exceedance. The daily average ozone concentration was 102.0 µg/m³. In contrast, nitrogen dioxide and particulate matter remained well within typical bounds. The maximum nitrogen dioxide concentration was 23.7 µg/m³, and the daily average was 9.4 µg/m³, both far below the 80 µg/m³ daily average limit. The maximum PM10 concentration was 31.4 µg/m³, with a daily average of 20.8 µg/m³, also below the 50 µg/m³ daily average threshold.

Comparing the day’s measurements to historical data since 2018, the ozone maximum of 148.9 µg/m³ was elevated but not extreme. It ranked 96th out of 2982 days in the all-time record, placing it within the top 4 percent of historical daily maxima. The absolute historical maximum for ozone remains 206.3 µg/m³, recorded on June 27, 2019. The nitrogen dioxide maximum of 23.7 µg/m³ was unremarkable, ranking 1718th historically. The PM10 maximum of 31.4 µg/m³ was also moderate, ranking 401st all-time, with the historical peak of 165.1 µg/m³ occurring on August 24, 2023.

Overall, the air quality on this day was characterized by a significant but not unprecedented ozone event, while other pollutants remained at low to moderate levels. The ozone exceedance was the primary feature of note, consistent with summertime conditions that favor photochemical ozone formation. The day’s ozone levels were above the seasonal average maximum of 175.8 µg/m³ but below the 30-day peak of 175.3 µg/m³, indicating a day of considerable but not record-setting ozone pollution.