SmogRank / Canada / Ontario / Cornwall
Cornwall, month by month
Cornwall has a measured daily mean on 1,066 days since 1 January 2023. Its worst month was June 2023, at 79 US AQI (24.2 µg/m³), 190th of 1,603 cities on that month's world ranking. Its cleanest was April 2024, at 19 US AQI (3.4 µg/m³). 2025 averaged 41 US AQI (7.3 µg/m³), against 52 US AQI (9.5 µg/m³) in 2023.
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
10 months
| Month | Why |
|---|---|
| Mar 2025 | 5 of 31 days measured; a month needs 22. The others: 26 with under 18 hours of readings or readings that failed our checks. |
| Feb 2025 | No day measured. The others: 28 with under 18 hours of readings or readings that failed our checks. |
| Jan 2025 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Dec 2024 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Nov 2024 | No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks. |
| Oct 2024 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Sep 2024 | No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks. |
| Aug 2024 | 14 of 31 days measured; a month needs 22. The others: 17 with under 18 hours of readings or readings that failed our checks. |
| Mar 2023 | 11 of 31 days measured; a month needs 22. The others: 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.
Cornwall's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| June 2023 | 7924.2 µg/m³ | 190thof 1,603 | Eastern United States and Canada, June and July 2023 United States and Canada, June 2023and 1 more |
| July 2025 | 5913.5 µg/m³ | 550thof 2,889 | North-eastern United States and Canada, 29 July to 9 August 2025 North-eastern United States and Canada, 24 to 28 July 2025and 1 more |
| July 2023 | 5812.7 µg/m³ | 316thof 1,432 | Northern United States and Canada, July 2023 United States and Canada, July 2023and 1 more |
| June 2025 | 5812.7 µg/m³ | 704thof 2,508 | Northern United States and Canada, May and June 2025 |
| July 2026 | 5511.1 µg/m³ | 1,089thof 2,784 | – |
| August 2025 | 5410.9 µg/m³ | 1,027thof 2,901 | North-eastern United States and Canada, 29 July to 9 August 2025 |
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.
Cornwall's worst days
| Day | US AQI | Episode |
|---|---|---|
| 25 Jun 2023 | 17995.8 µg/m³ | Eastern United States and Canada, June and July 2023 |
| 6 Jun 2023 | 17893.5 µg/m³ | Eastern United States and Canada, May and June 2023 |
| 26 Jun 2023 | 17286.0 µg/m³ | Eastern United States and Canada, June and July 2023 |
| 7 Jun 2023 | 17082.9 µg/m³ | Eastern United States and Canada, May and June 2023 |
| 6 Jun 2025 | 16170.3 µg/m³ | Northern United States and Canada, May and June 2025 |
| 30 Jun 2023 | 15764.0 µg/m³ | Eastern United States and Canada, June and July 2023 |
| 29 Jun 2023 | 13448.8 µg/m³ | Eastern United States and Canada, June and July 2023 |
| 7 Jun 2025 | 13448.8 µg/m³ | Northern United States and Canada, May and June 2025 |
| 15 Jul 2025 | 12244.0 µg/m³ | Northern United States and Canada, July 2025 |
| 1 Jul 2023 | 12143.7 µg/m³ | Eastern United States and Canada, June and July 2023 |
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, Cornwall, Canada, 1 Jan 2023 – 11 Oct 2026. Monitor data from AirNow, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/ca/cornwall/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.
Cornwall 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).