In April 2026, the air quality at the NBCN monitoring station in Binningen was generally favorable, with 3 days classified as KBI 1 (low pollution) and 23 days as KBI 2 (moderate pollution). There were 4 days with KBI 3 (marked pollution), and no days reached KBI 4 or higher. The KBI, or Kurzzeit-Belastungs-Index, is a short-term exposure index that combines the concentrations of ozone, nitrogen dioxide, and particulate matter into a single value to indicate the overall air pollution load. The mean concentrations for the month were 66.6 µg/m³ for ozone, 10.8 µg/m³ for nitrogen dioxide, and 12.1 µg/m³ for PM10, while the maximum concentrations reached 133.7 µg/m³ for ozone, 38.2 µg/m³ for nitrogen dioxide, and 36.3 µg/m³ for PM10. All values are listed in Table 1, and regulatory thresholds are listed in Table 3.

Comparing April 2026 with previous years, the month stands out for having the highest number of days with KBI 1 (rank 1 out of 8 years), indicating more days of low pollution than any other April since 2019. For KBI 2 days, it ranked lower, with 23 days compared to the 29 days seen in 2021, 2023, and 2024. In terms of maximum pollutant concentrations, April 2026 recorded the lowest maximum nitrogen dioxide level (rank 8), while its maximum ozone and PM10 levels ranked 5th and 6th, respectively. Overall, the air pollution in April 2026 was generally lower than in many previous years, particularly for nitrogen dioxide, and the monthly average and maximum values for April are reported in Table 2 and also displayed in Figures 1 to 3.