This report on air quality in Basel for August 24, 2023, 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 174.1 µg/m³, with an average of 99.65 µg/m³. Nitrogen dioxide (NO₂) had a maximum concentration of 20.3 µg/m³ and an average of 11.55 µg/m³. The particulate matter (PM2.5) recorded a maximum of 29.9 µg/m³ and an average of 13.28 µg/m³. The particle count (CPC) peaked at 15,324.9 particles/cm³, averaging 8,587.8 particles/cm³. Elemental carbon (EC) had a maximum of 0.6 µg/m³ and an average of 0.41 µg/m³. Sulfur dioxide (SO₂) reached a maximum of 1.0 µg/m³ with an average of 0.59 µg/m³. Nitrogen oxides (NOx) had a maximum of 25.1 µg/m³ and an average of 12.46 µg/m³.

When compared to historical data since 2018, the ozone levels on this day were unusually high, with the maximum value surpassing the highest recorded in the last 30 days and matching the seasonal maximum. NO₂ and PM2.5 levels were within the normal range, though slightly above the average for the last 30 days. The particle count and elemental carbon were also within typical ranges, though CPC was higher than the 30-day average. SO₂ levels were consistent with historical averages. NOx concentrations were slightly above average but did not reach historical maxima.

Overall, the air quality on August 24, 2023, showed unusual characteristics due to the significantly elevated ozone levels, which were higher than typical for this period. This anomaly could be attributed to specific weather conditions or increased emissions, warranting further investigation to understand the underlying causes and potential health implications.