SmogRank / Canada / Ontario / Guelph
Guelph, month by month
Guelph has a measured daily mean on 1,153 days since 13 July 2023. Its worst month was July 2026, at 80 US AQI (24.4 µg/m³), 228th of 2,784 cities on that month's world ranking. Its cleanest was October 2025, at 23 US AQI (4.2 µg/m³). 2025 averaged 41 US AQI (7.3 µg/m³), against 36 US AQI (6.5 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
1 month
| Month | Why |
|---|---|
| Jul 2023 | 17 of 31 days measured; a month needs 22. The others: 1 missing from OpenAQ's archive, 1 with under 18 hours of readings or readings that failed our checks. |
A day counts once 18 hours of it are measured; a month needs 70% of its days.
Guelph's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| July 2026 | 8024.4 µg/m³ | 228thof 2,784 | Northern United States and Canada, July 2026 |
| June 2025 | 5913.5 µg/m³ | 598thof 2,508 | Northern United States and Canada, May and June 2025 |
| August 2025 | 5813.0 µg/m³ | 579thof 2,901 | South-eastern Canada and United States, August 2025 North-eastern United States and Canada, 29 July to 9 August 2025 |
| July 2025 | 5712.4 µg/m³ | 753rdof 2,889 | North-eastern United States and Canada, 29 July to 9 August 2025 Northern United States and Canada, July 2025 |
| August 2023 | 5511.4 µg/m³ | 407thof 1,980 | Ontario, Canada, August 2023 |
| February 2026 | 529.8 µg/m³ | 1,455thof 2,866 | North-eastern United States and Canada, 14 to 19 February 2026 |
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.
Guelph's worst days
| Day | US AQI | Episode |
|---|---|---|
| 16 Jul 2026 | 256181.0 µg/m³ | Northern United States and Canada, July 2026 |
| 17 Jul 2026 | 235160.0 µg/m³ | Northern United States and Canada, July 2026 |
| 15 Jul 2026 | 16777.8 µg/m³ | Northern United States and Canada, July 2026 |
| 18 Jul 2026 | 15561.5 µg/m³ | Northern United States and Canada, July 2026 |
| 4 Aug 2025 | 15257.5 µg/m³ | North-eastern United States and Canada, 29 July to 9 August 2025 |
| 6 Jun 2025 | 14954.9 µg/m³ | Northern United States and Canada, May and June 2025 |
| 3 Aug 2025 | 13649.8 µg/m³ | North-eastern United States and Canada, 29 July to 9 August 2025 |
| 5 Jun 2025 | 12746.0 µg/m³ | Northern United States and Canada, May and June 2025 |
| 14 Jul 2025 | 12244.0 µg/m³ | Northern United States and Canada, July 2025 |
| 31 Jul 2025 | 11641.5 µg/m³ | North-eastern United States and Canada, 29 July to 9 August 2025 |
Daily means, the highest since 13 Jul 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, Guelph, Canada, 13 Jul 2023 – 11 Oct 2026. Monitor data from AirNow, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/ca/guelph/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.
Guelph now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 18:07 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).