This report on air quality in Basel for August 12, 2025, is published because the daily maximum ozone (O₃) concentration exceeded the 95th percentile of all values measured in August. On this day, the maximum O₃ concentration reached 171.1 µg/m³, with an average of 104.4 µg/m³. Nitrogen dioxide (NO₂) had a maximum concentration of 24.1 µg/m³ and an average of 11.4 µg/m³. Particulate matter (PM₂.₅) recorded a maximum of 21.4 µg/m³ and an average of 17.4 µg/m³. The particle count (CPC) peaked at 10,985.5 particles/cm³, averaging 6,423.9 particles/cm³. Elemental carbon (EC) had a maximum of 0.6 µg/m³ and an average of 0.45 µg/m³. Solar radiation reached a maximum of 800.2 W/m², averaging 280.6 W/m². Sulfur dioxide (SO₂) had a maximum of 2.9 µg/m³, with an average of 0.93 µg/m³. Nitrogen oxides (NOx) peaked at 29.3 µg/m³, averaging 12.9 µg/m³.

Comparing these values to historical data since 2018, the O₃ levels were unusually high, with the maximum value reaching the highest recorded for this season. The average O₃ concentration was significantly above the seasonal average of 74.61 µg/m³. NO₂ levels were within the normal range, with both maximum and average values below the seasonal maxima. PM₂.₅ concentrations were higher than the seasonal average but did not exceed historical maxima. The particle count was within typical ranges, with average values close to seasonal norms. EC levels were consistent with historical maxima. Solar radiation was within the normal range, not exceeding historical maxima. SO₂ levels were typical, with both average and maximum values below historical peaks. NOx concentrations were within normal ranges, with average values slightly above the seasonal average.

Overall, the air quality on August 12, 2025, showed some unusual characteristics, particularly with the elevated O₃ levels, which were significantly higher than historical norms. This could indicate specific atmospheric conditions or local emissions contributing to the spike. Other pollutants remained within typical ranges, suggesting that the overall air quality, while affected by high ozone levels, did not deviate drastically from historical norms for other parameters.