SmogRank / United States / Oregon / Ontario
Ontario, month by month
Ontario, Oregon has a measured daily mean on 1,280 days since 1 January 2023. Its worst month was July 2026, at 93 US AQI (31.9 µg/m³), 114th of 2,784 cities on that month's world ranking. Its cleanest was May 2024, at 16 US AQI (2.9 µg/m³). 2025 averaged 42 US AQI (7.5 µg/m³), against 39 US AQI (7.0 µg/m³) in 2024.
Every month since 2023
The US EPA's Air Quality Index for PM2.5 (2024 breakpoints). Show values as: µg/m³ · US AQI · India AQI · China AQI · European AQI · UK DAQI · Canada AQHI+. About the scales
Months without a mean, and why
2 months
| Month | Why |
|---|---|
| Mar 2023 | 9 of 31 days measured; a month needs 22. The others: 2 with readings for part of the day (a day needs 18 hours), 20 missing from OpenAQ's archive. |
| Feb 2023 | 3 of 28 days measured; a month needs 20. The others: 25 missing from OpenAQ's archive. |
A day counts once 18 hours of it are measured; a month needs 70% of its days.
Ontario's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| July 2026 | 9331.9 µg/m³ | 114thof 2,784 | North-western United States and Canada, July and August 2026 |
| August 2026 | 7120.0 µg/m³ | 243rdof 2,896 | North-western United States and Canada, 4 to 22 August 2026 North-western United States and Canada, July and August 2026 |
| January 2026 | 6416.1 µg/m³ | 695thof 2,617 | – |
| July 2024 | 6114.2 µg/m³ | 214thof 2,566 | North-western United States and Canada, July 2024 |
| January 2025 | 5812.9 µg/m³ | 626thof 2,474 | Western United States and Mexico, January and February 2025 |
| February 2026 | 5611.6 µg/m³ | 1,089thof 2,866 | – |
Monthly means over the days measured; finished months only. World rank: its place on that month's world ranking of every city with enough days. Each month opens that ranking.
Ontario's worst days
Daily means, the highest since 1 Jan 2023; the WHO's daily guideline is 15 µg/m³. Each date opens that day's world ranking, and each episode the bad-air spell it was part of.
Use this history
SmogRank, PM2.5 monthly and daily means, Ontario, Oregon, United States, 1 Jan 2023 – 10 Oct 2026. Monitor data from AirNow, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/us/ontario-oregon/history (accessed 12 Oct 2026).
You're welcome to reuse a single chart, image or figure with this citation and a link. Terms. Raw monitor readings in bulk are published by OpenAQ, under each provider's licence.
Ontario now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 17:07 UTC. Values are PM2.5 (fine particles), the median of each city's monitors, as the US AQI PM2.5 sub-index. Some low-cost readings: Sensor.Community, ODbL (data and licence). Some readings: Uzhydromet (Uzbekistan's Hydrometeorological Service); Department of Environment, Nepal; Vietnam's government monitors; Aurassure; Umhverfisstofnun (Environment Agency of Iceland); RMCAB (Secretaría Distrital de Ambiente, Bogotá); Love My Air (City and County of Denver), no reuse terms published (why we use them).