In September 2026, the air quality at the NBCN monitoring station in Binningen showed no days with a KBI of 1, meaning there were no days with low pollution. There were 23 days with a KBI of 2, indicating moderate pollution, and 7 days with a KBI of 3 or higher, which reflects marked or significant pollution. Specifically, 5 days reached KBI 3 and 2 days reached KBI 4. The KBI, or Kurzzeit-Belastungs-Index, combines the short-term exposure to ozone, nitrogen dioxide, and particulate matter into a single index that ranges from 1 (low) to 6 (very high). The mean concentrations for September 2026 were 68.1 µg/m³ for ozone, 9.7 µg/m³ for nitrogen dioxide, and 11.1 µg/m³ for PM10. The maximum concentrations were 137.0 µg/m³ for ozone, 43.3 µg/m³ for nitrogen dioxide, and 280.0 µg/m³ for PM10. All values are listed in Table 1, and regulatory thresholds are listed in Table 3.

Compared to previous Septembers from 2018 to 2025, September 2026 was generally more polluted in terms of ozone and PM10, but about average for nitrogen dioxide. The rank for days with KBI 1 was 8 out of 9 years, meaning only one year had fewer days with low pollution. For days with KBI 2, the rank was not directly provided, but the count of 23 days was similar to several previous years. The maximum ozone concentration ranked 5th highest out of 9 years, while the mean ozone concentration ranked 1st, making it the highest mean ozone for September in the dataset. The maximum nitrogen dioxide concentration ranked 4th, and the mean nitrogen dioxide ranked 6th. The maximum PM10 concentration ranked 1st, the highest recorded for September, driven by an extreme value of 280.0 µg/m³, while the mean PM10 ranked 5th. The monthly average and maximum values for September are reported in Table 2 and displayed in Figures 1 to 3.