SolriseAir Quality Index (AQI) explained
The Air Quality Index (AQI) is a 0 to 500 scale that turns pollutants like ozone and fine particles into one number for how harmful the air is to breathe. 0 to 50 is Good; above 100, sensitive groups should cut back on long outdoor exertion, and above 150, most people should.
What the AQI is
The Air Quality Index combines pollutants such as ground-level ozone and fine particulates (PM2.5) into one number. Rather than learning safe levels for each pollutant, you only need to read one scale: the higher the number, the more harmful the air. In the US, the scale and its colors are set by the Environmental Protection Agency.
The AQI scale
| AQI | Level | Color | What it means |
|---|---|---|---|
| 0 to 50 | Good | Green | Air quality is satisfactory, with little or no risk. |
| 51 to 100 | Moderate | Yellow | Acceptable, though unusually sensitive people may notice it. |
| 101 to 150 | Unhealthy for sensitive groups | Orange | People with asthma, heart or lung conditions, kids, and older adults may feel effects. |
| 151 to 200 | Unhealthy | Red | Anyone may begin to feel effects. Sensitive groups more seriously. |
| 201 to 300 | Very unhealthy | Purple | Health alert: increased risk for everyone. |
| 301 and up | Hazardous | Maroon | Emergency conditions. Everyone is likely to be affected. |
Source: US EPA Air Quality Index categories, colors, and health messages.
Why air quality changes
The AQI climbs with wildfire smoke, with vehicle exhaust trapped by stagnant air, and with ozone buildup on hot, sunny, windless days. Ozone forms in sunlight, so it usually peaks in the afternoon, which makes mornings the cleaner window on many summer days. Wind and rain tend to clean the air out; still, calm weather lets pollution pile up.
Visibility is a handy clue. Low visibility from smoke or haze is a good proxy for poor air quality, even if the AQI number has not updated yet.
What the AQI means for you
Everyday
Above 100, sensitive groups should cut back on prolonged outdoor exertion; above 150, most people should. On smoke days, an easy outdoor walk or run can put you through more polluted air per minute than you would think, so consider moving hard efforts indoors.
Outdoors
If the AQI is over 100, swap a hard run or ride for an easy one, or shorten it. Breathing harder pulls more pollution into your lungs. Since ozone usually peaks in the afternoon, an early start is often the simple fix.
Flying
Smoke and haze that drive AQI up can also drop visibility below the 3 statute miles drones need under Part 107. Never fly a drone near a wildfire: it can ground firefighting aircraft, and temporary flight restrictions often apply.
Common questions
What is a good AQI number?
0 to 50 is Good on the US EPA scale: air quality is satisfactory, with little or no risk. 51 to 100 is Moderate and acceptable for most people.
Is it safe to exercise outside when the AQI is over 100?
Above 100, sensitive groups should cut back on prolonged outdoor exertion, and above 150, most people should. Swapping a hard workout for an easy or indoor one is a simple fix.
Why is air quality worse in the afternoon?
Ground-level ozone builds up on hot, sunny, windless days and usually peaks in the afternoon, so mornings are often the cleaner window.
Related
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