Air pollution typically increases during winter due to temperature inversions, low wind speeds, and higher emissions from heating and traffic, which trap pollutants close to the ground. This leads to elevated concentrations of particulate matter, especially PM2.5, which rises more strongly than PM10 and remains longer in the air. Other pollutants such as nitrogen dioxide (NO₂) also tend to accumulate, while ozone (O₃) levels are usually lower due to reduced sunlight. These conditions often result in multi-day pollution episodes during cold, stagnant weather. Elevated levels of fine particles, particularly PM2.5, pose significant health risks, contributing to respiratory and cardiovascular diseases and increasing overall mortality. This insight summarizes the smog conditions during the past winter and compares it to historic data since 2018. For more information on smog, check out the data source reference or wikipedia

During the winter of 2025, the average concentration of nitrogen dioxide at the Binningen station was 21 micrograms per cubic meter, which is nearly double the baseline average of 11 micrograms per cubic meter observed during spring and fall. The average PM10 concentration was 13 micrograms per cubic meter in winter, compared to 12 micrograms per cubic meter during the baseline period. For PM2.5, the winter average was 12 micrograms per cubic meter, while the baseline average was 8 micrograms per cubic meter. The maximum values tell a more dramatic story: the winter maximum for PM10 reached 106 micrograms per cubic meter, far exceeding the baseline maximum of 58 micrograms per cubic meter. The winter maximum for PM2.5 was 89 micrograms per cubic meter, compared to a baseline maximum of 49 micrograms per cubic meter. These daily maximum and average values for NO2, PM10, and PM2.5 are plotted in Figures 1 and 2. A prominent peak in fine particle concentrations occurred at the end of December, which is likely caused by the New Year's fireworks.

Looking at the yearly data from 2018 to 2025, the average winter PM10 concentration has fluctuated between 12 and 17 micrograms per cubic meter, with no clear long-term trend. The winter maximum PM10 values have ranged from 51 to 106 micrograms per cubic meter, with the highest value recorded in 2025. For PM2.5, the winter average has varied between 10 and 14 micrograms per cubic meter, and the winter maximum has ranged from 40 to 89 micrograms per cubic meter, also peaking in 2025. The baseline averages for both PM10 and PM2.5 have remained relatively stable, typically between 11 and 14 micrograms per cubic meter for PM10 and between 7 and 10 micrograms per cubic meter for PM2.5. The baseline maximum values have shown more variability, with a notable spike for PM10 in 2023 reaching 165 micrograms per cubic meter. Overall, the data does not indicate a clear increasing or decreasing trend for winter particulate matter concentrations over this period, but the winter of 2025 stands out for its high maximum values for both PM10 and PM2.5.