On 2026-05-30, ozone was the primary air quality concern in Basel. The maximum ozone concentration reached 139.3 µg/m³, which exceeded the regulatory threshold of 120.0 µg/m³. This value ranked 19th highest among the last 365 days. The average ozone concentration for the day was 99.1 µg/m³, which is notably higher than the 30-day average of 75.2 µg/m³ and the seasonal average of 65.9 µg/m³.

Nitrogen dioxide levels remained low, with a maximum of 13.5 µg/m³ and an average of 7.8 µg/m³. These values are well below the regulatory limit of 80.0 µg/m³ and are consistent with recent averages. The maximum NO₂ concentration ranked 301st out of the last 366 days, indicating it was not elevated.

Fine particulate matter (PM10) concentrations were moderate, with a maximum of 27.2 µg/m³ and an average of 17.5 µg/m³. Both values are below the regulatory threshold of 50.0 µg/m³. The average PM10 concentration was slightly above the 30-day average of 12.7 µg/m³ and the seasonal average of 13.8 µg/m³. The maximum PM10 concentration ranked 67th over the past year.

Comparing the current values to historical data since 2018, the maximum ozone concentration of 139.3 µg/m³ is well below the all-time maximum of 206.3 µg/m³ recorded on June 27, 2019. The maximum NO₂ concentration of 13.5 µg/m³ is far below the historical maximum of 83.2 µg/m³ from February 15, 2019. The maximum PM10 concentration of 27.2 µg/m³ is also significantly lower than the all-time maximum of 165.1 µg/m³ recorded on August 24, 2023.

Overall, air quality on 2026-05-30 was characterized by elevated ozone levels, which exceeded regulatory standards and were significantly above typical seasonal and recent averages. This suggests a day with strong photochemical activity, likely driven by high temperatures and abundant sunlight. Nitrogen dioxide and PM10 levels remained within normal ranges and did not pose a concern.