On July 16, 2026, air quality in Basel was characterized by elevated ozone levels. The maximum ozone concentration of 153.4 µg/m³ ranked 11th highest among the last 365 days, indicating a notably high value for the recent period. This concentration exceeded the regulatory threshold of 120.0 µg/m³ for the maximum hourly average, as defined by the Swiss Clean Air Ordinance.

The average ozone concentration for the day was 93.7 µg/m³, which is above the seasonal average of 83.9 µg/m³ for this time of year. The maximum value of 153.4 µg/m³ was below the all-time maximum of 206.3 µg/m³ recorded on June 27, 2019, and also below the 30-day maximum of 175.8 µg/m³. While elevated, the ozone levels were not unprecedented for the summer season.

Nitrogen dioxide and PM10 concentrations remained low. The average NO2 concentration was 8.3 µg/m³, with a maximum of 17.1 µg/m³, both well below the regulatory daily average limit of 80.0 µg/m³. The average PM10 concentration was 11.9 µg/m³, with a maximum of 18.3 µg/m³, also far below the daily average limit of 50.0 µg/m³. These values are consistent with typical summer conditions, when pollutant levels from traffic and heating are generally lower.

Overall, the air quality on this day was unusual due to the elevated ozone, which reached a level that triggered an exceedance of the regulatory standard. The high ozone is typical for a warm, sunny summer day with strong photochemical activity. The low NO2 and PM10 concentrations are consistent with reduced emissions from traffic and the absence of winter heating sources.