On July 29, 2026, ozone was the primary pollutant of concern in Basel. The maximum ozone concentration reached 159.9 µg/m³, which ranked as the 9th highest daily maximum in the past 365 days. This value exceeded the regulatory threshold of 120 µg/m³ for the maximum hourly average. The daily average ozone concentration was 110.6 µg/m³. In contrast, nitrogen dioxide and particulate matter remained well within typical limits. The maximum nitrogen dioxide reading was 21.0 µg/m³ and the daily average was 8.3 µg/m³, both far below the 80 µg/m³ daily average threshold. For PM10, the maximum was 27.9 µg/m³ and the average was 17.2 µg/m³, also below the 50 µg/m³ daily average limit.

Compared to recent weeks and the current season, the ozone levels on this day were elevated. The daily maximum of 159.9 µg/m³ was higher than the average maximum of 175.3 µg/m³ seen over the last 30 days, but the average ozone concentration of 110.6 µg/m³ was above both the 30-day average of 95.5 µg/m³ and the seasonal average of 86.9 µg/m³. Nitrogen dioxide and PM10 values were close to their typical recent averages. Looking at the long-term historical record since 2018, the ozone maximum of 159.9 µg/m³ ranked 40th out of 2,977 days, placing it within the top 2 percent of all daily maxima. The absolute historical maximum for ozone remains 206.3 µg/m³, recorded on June 27, 2019.

Overall, the air quality on July 29, 2026, was characterized by a notable ozone episode, while other pollutants remained unremarkable. The elevated ozone concentrations were consistent with summertime conditions favorable for photochemical production. This event, while significant for the day, did not approach the extreme historical peak observed in 2019.