LIVE • 2026-07-11
Highest O3 cities right now
Top 30 cities ranked by current O3 concentration across all 217 tracked locations. Refreshes every 30 minutes. The highest O3 right now is in Rio de Janeiro, Brazil at 159.0 ppb. WHO 2021 8-hour guideline: 100 μg/m³ (~50 ppb).
About O3
See the full O3 guide for sources, health effects, and mitigation. Or jump back to overall most polluted cities ranked by US EPA Air Quality Index.
See also: highest PM2.5 · highest PM10 · highest NO2