This report on air quality in Basel for June 27, 2019, is published because the daily maximum ozone (O₃) concentration exceeded the 95th percentile of all values measured in June. On this day, the maximum O₃ concentration was 206.3 µg/m³, with an average of 124.8 µg/m³. Nitrogen dioxide (NO₂) levels reached a maximum of 20.8 µg/m³, with an average of 14.6 µg/m³. Particulate matter (PM₂.₅) had a maximum concentration of 28.8 µg/m³ and an average of 22.3 µg/m³. The particle count (CPC) peaked at 21,633.3 particles/cm³, averaging 11,807.6 particles/cm³. Elemental carbon (EC) recorded a maximum of 2.5 µg/m³, with an average of 0.64 µg/m³. Sulfur dioxide (SO₂) reached a maximum of 4.8 µg/m³, averaging 1.5 µg/m³. Nitrogen oxides (NOx) had a maximum of 23.4 µg/m³, with an average of 15.8 µg/m³.

Comparing these values to historical data since 2018, the O₃ levels on June 27 were unusually high, with the maximum value reaching the highest recorded for this season. The average O₃ concentration was significantly above the typical seasonal average of 76.48 µg/m³. NO₂ levels were within the normal range, with both maximum and average values below historical peaks. PM₂.₅ concentrations were higher than the seasonal average of 7.08 µg/m³, but within the historical maximum range. CPC values were typical, with averages aligning closely with historical data. EC levels were slightly above the average but did not exceed historical maxima. SO₂ concentrations were within normal historical ranges. NOx levels were slightly above average but did not reach historical peaks.

In conclusion, the air quality on June 27, 2019, showed unusual characteristics, particularly with the elevated O₃ levels, which were significantly higher than typical values for this time of year. This spike in ozone could be attributed to specific weather conditions or increased emissions, warranting further investigation. Other pollutants remained within expected ranges, indicating that the primary concern for this day was the elevated ozone concentration.