Air quality in Ontario
Most recent reading from the official reporting area covering Ontario.
Preliminary readings from official networks, not fully validated. For health decisions follow your doctor and your local environmental agency.
AQI
—
NW San Bernardino, CA ·
Main pollutant
—
South Coast AQMD
What to do
—
Forecast
| Day | AQI | Category | Main pollutant |
|---|---|---|---|
| 10/15/26 | 41 | Good | OZONE |
| 10/16/26 | 33 | Good | PM2.5 |
Index
| Range | What to do |
|---|---|
| Good (0 to 50) | No health risk expected. |
| Moderate (51 to 100) | Unusually sensitive people may cut back on outdoor effort. |
| Unhealthy for sensitive groups (101 to 150) | Children, older adults and people with asthma or heart disease should reduce hard outdoor activity. |
| Unhealthy (151 to 200) | Everyone may feel effects; sensitive groups should stay indoors. |
| Very unhealthy (201 to 300) | Health alert: avoid outdoor exertion. |
| Hazardous (above 300) | Emergency conditions: stay in filtered air. |
Choose a city
- Upland76,443 inhabitants
- Chino85,595 inhabitants
- Rancho Cucamonga175,236 inhabitants
- Pomona153,266 inhabitants
- Chino Hills78,309 inhabitants
- Eastvale59,039 inhabitants
How to read this page
How to read the AQI
Up to 50 the air is good, up to 100 moderate, above 100 it starts affecting sensitive groups. The Ontario score reports the worst pollutant of the moment, not the average of all of them.
Where the data comes from
The reading comes from the AirNow public archive (U.S. EPA), measured by South Coast AQMD, at the NW San Bernardino, CA monitor.
Preliminary data, and distance
AirNow publishes measurements without final validation, not valid for regulatory use. And the monitor is not inside Ontario: treat the number as an order of magnitude, not as a measure of your street.
What to do with a high index
With an index above 100, cut outdoor effort, close windows facing busy roads and follow the official band-by-band advice on the AirNow site.
Understanding air quality in Ontario
Is the air in Ontario good right now?
No reference monitor near Ontario has a valid reading at the moment. The page stays up because coverage changes: as soon as the agency publishes a value for the area it appears at the top.
Words on this page
AQI
The United States Air Quality Index, 0 to 500, which converts each pollutant concentration into a single score and reports the worst one. Up to 50 is good, above 100 it starts to affect sensitive groups, above 150 it affects everyone. The score is not linear in concentration: it follows breakpoints set by the EPA.
Standard definition by U.S. EPA — AQI Technical Assistance Document · AQI
PM2.5
Particulate matter under 2.5 micrometres across, fine enough to reach the depths of the lung. It is the pollutant that most often sets the AQI, and it comes from burning: diesel engines, fire, wood stoves, industry.
Standard definition by U.S. EPA — AQI Technical Assistance Document · PM2.5
Ground-level ozone
Ozone formed near the ground when sunlight reacts with exhaust gases and solvents. It is not the ozone layer, which sits kilometres up and protects us: this one irritates the airways and rises on clear, hot, windless days.
Standard definition by U.S. EPA — AQI Technical Assistance Document · Ground-level ozone
UV index
An open-ended scale starting at 0 that measures the strength of ultraviolet radiation able to redden skin. From 3 to 5 protection is already advised, 8 to 10 is very high and above 11 is extreme. It depends on how high the Sun is, on the ozone layer, on altitude and on cloud.
Standard definition by WHO / WMO — Global Solar UV Index · UV index
Preliminary data
A measurement published as soon as it is collected, before the agency’s final review. It can be corrected or withdrawn: earthquake magnitudes shift in the first hours, air-quality readings are revised weeks later. Use it to plan your day, not for regulatory or legal purposes.
Data from 10/16/26, 6:07 AM UTC
- U.S. EPA AirNow (áreas de referência, arquivo público)Licence: Dado público da EPA, sujeito às AirNow Data Use Guidelines (atribuição obrigatória) · Credit: U.S. EPA AirNow e a agência estadual, tribal ou local que fez a mediçãoDados preliminares, sem validação final; não servem para fins regulatórios.
- GeoNames cities15000Licence: CC BY 4.0 · Credit: Dados de cidades: GeoNames (CC BY 4.0)
- Dados de cidades: GeoNames (CC BY 4.0)
How to read these numbers
The value is preliminary: networks publish a reading within about an hour and validate it later. It is good for deciding whether to go running today, not for legal comparison between years.
Frequently asked questions
- What is the air quality in Ontario right now?
- The large number at the top is the latest reading from the reporting area that includes Ontario, with the observation time beside it.
- What about tomorrow?
- Where the agency publishes a forecast, it appears in the day table. Forecasts are made by the network’s own meteorologists with a dispersion model.
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