On July 20, 2025, the air quality in Basel was characterized by moderate levels of pollutants. The maximum ozone (O₃) concentration reached 93.5 µg/m³, with an average of 61.75 µg/m³. Nitrogen dioxide (NO₂) levels were relatively low, with a maximum of 12.8 µg/m³ and an average of 6.85 µg/m³. Particulate matter (PM2.5) concentrations were also low, peaking at 7.7 µg/m³ and averaging 5.85 µg/m³. The particle count (CPC) was higher, with a maximum of 11,250.7 particles/cm³ and an average of 5,994.92 particles/cm³. Elemental carbon (EC) had a maximum concentration of 0.3 µg/m³ and an average of 0.18 µg/m³. Sulfur dioxide (SO₂) levels were minimal, with a maximum of 0.4 µg/m³ and an average of 0.2 µg/m³. Nitrogen oxides (NOx) were recorded at a maximum of 13.8 µg/m³ and an average of 8.19 µg/m³.

Comparing these values to historical data since 2018, the ozone levels on this day were below the recent 30-day average of 82.66 µg/m³ and the seasonal average of 78.44 µg/m³. NO₂ levels were slightly below both the recent 30-day average of 6.91 µg/m³ and the seasonal average of 7.33 µg/m³. PM2.5 concentrations were lower than the 30-day average of 7.33 µg/m³ and the seasonal average of 8.81 µg/m³. The particle count was below the 30-day average of 6,635.76 particles/cm³ and the seasonal average of 6,785.27 particles/cm³. EC levels were consistent with the 30-day average of 0.2 µg/m³ but slightly below the seasonal average of 0.23 µg/m³. SO₂ levels were significantly lower than both the 30-day average of 0.45 µg/m³ and the seasonal average of 0.49 µg/m³. NOx levels were slightly above the 30-day average of 7.93 µg/m³ but below the seasonal average of 8.34 µg/m³.

Overall, the air quality on July 20, 2025, was within the typical range observed historically, with no pollutants exceeding their respective thresholds or historical maxima. The slightly elevated particle count compared to historical averages could be of interest, but it did not reach concerning levels. The low levels of NO₂ and SO₂ suggest favorable conditions for air quality, possibly due to meteorological factors or reduced emissions on that day.