Air quality
Air quality in St. Thomas today
Updated
Good (US AQI 38) Air quality is satisfactory and poses little or no risk; a good time for outdoor activity. Model estimate for Sun, Oct 25, 10:00 pm (02:00 UTC).
Live AQI, PM2.5, PM10 and ozone for St. Thomas, Ontario, Canada, with a 48-hour forecast and the best time to be outside.
- US AQI now
- 38 Good
- PM2.5
- 11 µg/m³ 0.8× WHO 24-h guideline
- PM10
- 11 µg/m³
- Ozone
- 73 µg/m³
- Dominant pollutant
- ozone sub-index 38
- Best hour tomorrow
- 6:00 am AQI 44
- European AQI
- 33
Air quality in St. Thomas right now
Right now the modelled US Air Quality Index for St. Thomas, Ontario, Canada is 38, which falls in the "Good" band (up to 50). Air quality is satisfactory and poses little or no risk; a good time for outdoor activity.
The index is driven mainly by ozone, whose own sub-index is 38. Ozone usually peaks in the afternoon on sunny days and falls back after sunset.
PM2.5 is 11 µg/m³, within the WHO 24-hour guideline of 15 µg/m³; PM10 is 11 µg/m³ against a guideline of 45; ozone is 73 µg/m³ (below the WHO 8-hour level of 100); nitrogen dioxide is 11 µg/m³ (below the 24-hour guideline of 25).
Also this hour: carbon monoxide 222 µg/m³.
NASA FIRMS shows 96 fire hotspots within 300 km in the last day (nearest about 13 km), but particle levels are not elevated enough to point to smoke right now.
St. Thomas AQI forecast: next 48 hours
Over the next 24 hours the AQI is forecast to range from 36 around Mon 12:00 am to 58 around Mon 2:00 pm, from "Good" at best to "Moderate" at worst.
The following day is expected to be cleaner, averaging about 35 against 49 for the next 24 hours.
| Local time (America/Toronto) | US AQI | Category | PM2.5 µg/m³ | PM10 µg/m³ | Ozone µg/m³ |
|---|---|---|---|---|---|
| Sun 10:00 pm | 38 | Good | 11.4 | 11 | 73 |
| Mon 1:00 am | 36 | Good | 11.1 | 11 | 78 |
| Mon 4:00 am | 40 | Good | 13 | 13 | 71 |
| Mon 7:00 am | 47 | Good | 18.4 | 18 | 49 |
| Mon 10:00 am | 53 | Moderate | 24.4 | 24 | 43 |
| Mon 1:00 pm | 57 | Moderate | 11.2 | 11 | 68 |
| Mon 4:00 pm | 58 | Moderate | 3.9 | 4 | 78 |
| Mon 7:00 pm | 57 | Moderate | 1.7 | 2 | 64 |
| Mon 10:00 pm | 55 | Moderate | 1.6 | 2 | 54 |
| Tue 1:00 am | 53 | Moderate | 1.8 | 2 | 48 |
| Tue 4:00 am | 50 | Good | 1.8 | 2 | 43 |
| Tue 7:00 am | 42 | Good | 1.9 | 2 | 37 |
| Tue 10:00 am | 29 | Good | 2.6 | 3 | 38 |
| Tue 1:00 pm | 18 | Good | 1.6 | 2 | 52 |
| Tue 4:00 pm | 21 | Good | 1.5 | 2 | 59 |
| Tue 7:00 pm | 25 | Good | 2.6 | 3 | 48 |
| Tue 10:00 pm | 24 | Good | 2.9 | 3 | 41 |
Every third hour of the CAMS forecast via Open-Meteo. US AQI uses rolling averages (24 h for particles, 8 h for ozone), so it moves more slowly than the hourly concentrations.
Best time to be outside in St. Thomas tomorrow
Between 6 am and 9 pm local time, the cleanest air tomorrow is forecast around 6:00 am (AQI 44, Good) and the worst around 2:00 pm (AQI 58). That is a swing of 14 points, so a run or walk around 6:00 am is noticeably better.
St. Thomas vs the rest of Canada
Across 75 Canada cities we track, the average US AQI right now is 44 (Good). St. Thomas at 38 is 6 points cleaner than average.
It ranks 30 of 75 from cleanest to most polluted; the cleanest is Surrey (26) and the most polluted Windsor (78).
For context, the median across 3,556 cities worldwide is 58.
Air quality in cities near St. Thomas
| City | Distance | US AQI | Category | PM2.5 µg/m³ |
|---|---|---|---|---|
| London, ON | 24 km | 41 | Good | 11.1 |
| Brantford | 84 km | 48 | Good | 12.9 |
| Kitchener | 91 km | 51 | Moderate | 13.1 |
| Waterloo | 94 km | 51 | Moderate | 13.1 |
| Cambridge, ON | 96 km | 48 | Good | 12.9 |
| Sarnia | 102 km | 55 | Moderate | 14.2 |
| Port Huron | 104 km | 55 | Moderate | 14.2 |
| Erie | 115 km | 42 | Good | 12.5 |
Model vs measured
We found no measured PM2.5 sensor cell within 25 km of St. Thomas, so the numbers on this page are model estimates. Models capture regional pollution well but can miss very local sources such as a busy road or a nearby fire.
Advice for sensitive groups
With the AQI at 38, there is no need for sensitive groups to change plans. People with asthma should still carry their reliever inhaler as usual.
What the US AQI numbers mean
| US AQI | Category | What it means |
|---|---|---|
| 0-50 | Good | Air quality is satisfactory and poses little or no risk; a good time for outdoor activity. |
| 51-100 | Moderate | Acceptable for most people. Unusually sensitive people should consider shortening long or heavy exertion outdoors. |
| 101-150 | Unhealthy for Sensitive Groups | People with heart or lung disease, older adults, children and teens should cut back on prolonged or heavy exertion outdoors. |
| 151-200 | Unhealthy | Everyone should reduce prolonged or heavy exertion outdoors; sensitive groups should avoid it and keep windows closed. |
| 201-300 | Very Unhealthy | Health alert: everyone should avoid prolonged or heavy exertion outdoors, and sensitive groups should stay indoors. |
| 301-500 | Hazardous | Emergency conditions: everyone should avoid all outdoor physical activity and stay indoors with filtered air if possible. The scale tops out at 500; heavier dust or smoke is shown as 500. |
Values on this page are modelled by CAMS (Copernicus) and served by Open-Meteo; they are estimates for the area around the city centre, not readings from an official monitor.
Nearby cities
More for St. Thomas
Air quality elsewhere
Data: Open-Meteo Air Quality API, Copernicus Atmosphere Monitoring Service (CAMS), NASA FIRMS.