On 2026-09-28, ozone was the only measured pollutant to exceed its regulatory threshold. The maximum hourly ozone concentration reached 137.0 µg/m³, above the Swiss limit of 120.0 µg/m³, while the daily average was 86.2 µg/m³. Nitrogen dioxide and PM10 remained well below their respective limits, with maximum values of 29.6 µg/m³ and 31.0 µg/m³, and daily averages of 14.5 µg/m³ and 18.6 µg/m³. The overall air quality rating was “considerable,” driven entirely by the ozone exceedance.

Compared with the past 365 days, the maximum ozone value ranked 36th out of 362 days, placing it in the top 10 percent of recent readings but not among the very highest. The maximum NO2 value ranked 125th, and the maximum PM10 value ranked 56th, both unremarkable for the period. Relative to the last 30 days, the day’s ozone maximum of 137.0 µg/m³ was almost identical to the 30-day maximum of 136.5 µg/m³, while the daily average of 86.2 µg/m³ was well above the 30-day average of 66.1 µg/m³. NO2 and PM10 averages were also above their 30-day averages, but their maxima were below the 30-day maxima.

Historical comparison since 2018 shows that the ozone maximum of 137.0 µg/m³ ranked 200th out of 3038 days, placing it in the top 7 percent of all daily maxima but far below the all-time maximum of 206.3 µg/m³ recorded on 2019-06-27. The NO2 maximum ranked 1298th, and the PM10 maximum ranked 427th, both within typical historical ranges. The all-time PM10 maximum of 580.2 µg/m³ occurred on 2026-08-15, but the value on 2026-09-28 was not close to that extreme.

Overall, air quality on 2026-09-28 was dominated by moderately elevated ozone, consistent with warm-season photochemical conditions. The ozone exceedance was notable but not exceptional for late September, and it did not approach the highest values seen in recent years or the historical record. NO2 and PM10 remained unremarkable. The day’s air quality was therefore somewhat worse than a typical day due to ozone, but not an extreme pollution event.