On August 15, 2025, the air quality in Basel was notably affected by elevated levels of ozone (O₃). The maximum concentration of ozone reached 170.4 µg/m³, which is significantly above the regulatory threshold of 120 µg/m³ set by the Luftreinhalte-Verordnung and marked an exceedance. This value ranks 3rd in the past 365 days, indicating a particularly high level for the year. The average ozone concentration was 108.7 µg/m³, also elevated compared to recent averages.

Nitrogen dioxide (NO₂) levels were relatively low, with a maximum concentration of 27.8 µg/m³ and an average of 11.4 µg/m³, both well below the regulatory threshold of 80 µg/m³. These values are consistent with typical levels observed in Basel and do not indicate any exceedance.

Particulate matter (PM₁₀) concentrations were moderate, with a maximum of 46.8 µg/m³ and an average of 33.2 µg/m³. While these values are below the regulatory threshold of 50 µg/m³, the maximum concentration ranks 11th in the past 365 days, suggesting a relatively high level for the year.

Comparing these measurements with historical data since 2018, the current ozone levels are unusually high, with the maximum value approaching the historical maximum of 206.3 µg/m³ recorded on June 27, 2019. The nitrogen dioxide and particulate matter levels are within normal historical ranges, with no significant anomalies.

Overall, the air quality on August 15, 2025, was characterized by unusually high ozone concentrations, which were significantly above both recent and historical averages. This suggests an atypical air quality event, likely influenced by specific meteorological conditions or local emissions. The elevated ozone levels are of particular concern due to their potential health impacts, warranting attention to potential sources and mitigation strategies.