On 2026-08-14, air quality in Basel was dominated by elevated ozone and fine particulate matter. Ozone reached a maximum hourly concentration of 164.4 µg/m³, exceeding the regulatory threshold of 120 µg/m³, and its daily average was 118.8 µg/m³. This maximum ranked 8th among the past 365 days, indicating a notably high value. PM10 reached a maximum of 80.5 µg/m³, which ranked 4th over the same period, although its daily average of 24.2 µg/m³ remained below the 50 µg/m³ daily average threshold. Nitrogen dioxide was unremarkable, with a maximum of 28.6 µg/m³ and an average of 9.5 µg/m³, both far below the 80 µg/m³ daily average limit.

Compared with the previous 30 days, the ozone average of 118.8 µg/m³ was above the 30-day average of 99.3 µg/m³, and the maximum of 164.4 µg/m³ approached the 30-day maximum of 175.3 µg/m³. PM10 showed a sharper contrast: its maximum of 80.5 µg/m³ exceeded the 30-day maximum of 63.2 µg/m³ and was well above the 30-day average mean of 15.9 µg/m³. Relative to the current season, ozone was also above the seasonal average mean of 90.3 µg/m³, while PM10 was above the seasonal average mean of 14.6 µg/m³ and matched the seasonal maximum of 80.5 µg/m³. NO2 remained close to its recent and seasonal averages.

Looking at the full historical record since 2018, the ozone maximum of 164.4 µg/m³ ranked 31st out of 2993 days, placing it in the top roughly one percent of all daily maxima. The all-time ozone maximum was 206.3 µg/m³ on 2019-06-27. The PM10 maximum of 80.5 µg/m³ ranked 15th out of 2993 days, also within the top one percent historically. The all-time PM10 maximum was 165.1 µg/m³ on 2023-08-24. NO2 was far from any historical extreme, ranking 1361st.

Overall, the air quality on 2026-08-14 was unusual due to simultaneous elevated ozone and PM10. Ozone exceeded its regulatory threshold and ranked among the highest values of the past year, while PM10 reached a level rarely seen in the historical record, even though its daily average stayed below the legal limit. The combination suggests a day with strong photochemical activity and likely a source of coarse particles, such as regional transport or local resuspension. Nitrogen dioxide remained low, consistent with warm-season conditions and reduced traffic-related emissions.