Understanding Outdoor Air Quality
The Air Quality Index (AQI) is a simple way to describe how polluted the outdoor air is and when air pollution may become a health concern.
The higher the AQI number, the greater the level of air pollution and the potential health concern.
What does the AQI number mean?
The WHN air-quality widget uses the U.S. EPA AQI scale everywhere, giving visitors a consistent scale regardless of location. Other countries and services may use different AQI systems, so their numbers may not always be identical.
Good
Air quality is satisfactory and air pollution poses little or no risk.
Moderate
Air quality is generally acceptable, although some unusually sensitive people may be affected.
Unhealthy for sensitive groups
People who are more vulnerable to air pollution may experience health effects.
Unhealthy
Some health effects may occur in the general public, with greater risk for sensitive groups.
Very unhealthy
The risk of health effects is increased for everyone.
Hazardous
Emergency-level air pollution conditions. Everyone is more likely to be affected.
AQI is a useful snapshot, not a complete measure of your exposure. Air pollution can change over time and over short distances, and repeated or long-term exposure also matters.
What are PM2.5 and PM10?
PM2.5 and PM10 are concentrations, not separate AQI scores. They tell you how much particle pollution is in the air, measured in µg/m³ (micrograms per cubic meter). Particle concentrations can be used to determine an AQI, but the values will not always correspond exactly to the AQI shown by the widget. This is because AQI calculations may use time-averaged measurements, and some data sources provide an overall AQI that can also reflect other pollutants.
PM2.5
PM2.5 refers to airborne particles with a diameter of 2.5 micrometers or smaller. They can come from sources such as smoke and combustion, as well as chemical reactions in the atmosphere.
Because these particles are so small, they can travel deep into the lungs, and some can enter the bloodstream.
The widget reports PM2.5 in µg/m³ — micrograms of particles per cubic meter of air.
For example, a current PM2.5 reading of 4.5 µg/m³ is in the Good range.
PM10
PM10 refers to airborne particles with a diameter of 10 micrometers or smaller. It includes PM2.5 as well as larger inhalable particles such as some dust and smoke.
PM10 particles can enter the respiratory system, while the smaller PM2.5 particles can generally penetrate farther into the body.
PM10 is also reported in µg/m³.
Seeing “—” for PM10? Not every monitoring station or data source reports PM10. A dash means that PM10 is not available from the source being used — not that the concentration is zero.
Where does the air-quality information come from?
The WHN widget uses several sources so that it can provide useful local air-quality information in as many places as possible.
When suitable recent measurements are available, we prefer ground-level monitoring data. These may come from official reference monitoring stations or, where appropriate, nearby community air-quality sensors. We currently access these measurements through OpenAQ, which brings together air-quality measurements from monitoring networks around the world.
If suitable nearby measurements are not available, the widget may use a local air-quality result from IQAir / AirVisual.
If neither source can provide a suitable current result, the widget falls back to modeled outdoor air-quality information from Open-Meteo, using data from the Copernicus Atmosphere Monitoring Service (CAMS). These modeled estimates provide broad worldwide coverage, but conditions at your exact location can differ, particularly near fires, busy roads or other local sources of pollution.
The source used for your current result is always shown at the bottom of the widget.
When the widget uses nearby PM2.5 or PM10 measurements, it may display an approximate U.S. EPA particle AQI calculated from the current particulate measurement. When IQAir supplies the result, the widget displays the U.S. AQI provided by IQAir.
Location and privacy
Your precise location is optional
When the widget first loads, it does not request your device’s precise location. Instead, the WHN website uses your internet address to estimate your general location, such as your city or region.
To make this approximate lookup, the WHN server currently sends the internet address to the geolocation service ipwho.is. The widget uses a keyed hash rather than the raw internet address as the identifier for its location cache in WordPress.
If you select “Use my precise location” or “Refresh precise location”, your browser will first ask for permission. Nothing is shared through this feature unless you grant that permission.
If permission is granted, the coordinates supplied by your browser are sent to the WHN website, which uses them to request air-quality information from the applicable data source. They are also sent from your browser to BigDataCloud so that the coordinates can be converted into a recognizable place name such as a city or town.
You do not need to use precise location. You can decline the browser request and continue using the approximate-location estimate.
