On 2026-08-15, air quality in Basel was dominated by an exceptional PM10 event. The maximum PM10 concentration reached 580.2 µg/m³, which ranks as the highest value recorded in the past 365 days and the fourth highest since 2018. The daily average PM10 was 59.2 µg/m³, exceeding the regulatory daily average threshold of 50 µg/m³. The minimum PM10 value of 14.1 µg/m³ indicates that the extreme peak was likely short-lived or localized, but the overall daily average still breached the legal limit.

Ozone also exceeded its regulatory threshold. The maximum ozone concentration was 156.4 µg/m³, above the 120 µg/m³ standard, and the daily average was 120.1 µg/m³. This maximum ranks 15th among the past 365 days, placing it in the top 5 percent of recent daily maxima. Compared with the last 30 days, the average ozone level was higher than the 30-day average of 99.5 µg/m³, and the maximum was below the 30-day peak of 168.0 µg/m³. Nitrogen dioxide remained unremarkable, with a maximum of 16.4 µg/m³ and an average of 7.9 µg/m³, both far below the 80 µg/m³ daily average threshold and consistent with recent 30-day and seasonal averages.

The PM10 maximum of 580.2 µg/m³ is the same value recorded as the all-time maximum for PM10 in the dataset, and its date is listed as 2026-08-15, meaning this day set or matched the historical record. The seasonal average PM10 maximum was also 580.2 µg/m³, confirming that this single day drove the seasonal extreme. In contrast, the 30-day average PM10 maximum was only 80.5 µg/m³, so the current value is more than seven times higher than the recent monthly peak. The rank of 1 in the last 365 days and rank of 4 in all 2,994 days of data underscore how unusual this PM10 level was.

Overall, air quality on 2026-08-15 was not consistent with historical norms. The PM10 exceedance was extreme and likely caused by a discrete event such as a dust storm, construction activity, fire, or industrial release rather than a broad regional pollution episode, given the low minimum value and the otherwise moderate average. Ozone was elevated but within the range of occasional summer exceedances. Nitrogen dioxide was unremarkable. The day should be flagged as an anomaly primarily due to the record-level PM10 spike.