What are air quality scales?
Air quality stations measure concentrations of pollutants in each country or region. Countries or regions define air quality indexes and categorize the raw data into a descriptive rating scale. These indexes make it easier to identify the level of pollution and if there’s any associated risk.
Different countries/regions use different scales to report air quality based on local pollution and health considerations. There are dozens of local indexes used across the globe. For example, some states in Australia use a number-based system while others use a category-based system. Canada, US, and Japan define separate air quality indexes, as does the European Environment Agency.
As the air pollution worsens, public health risks increase. It especially affects children, the older adult population, and other at-risk populations. During times of poor air quality, governmental agencies generally provide health recommendations related to indoor and outdoor activities.
How air quality indexes are calculated
The Air Quality local Indexes are based on measurements of air pollutants.
Some common pollutants that are tracked include:
- Particulate matter, like PM2.5 and PM10
- Ozone (O3)
- Nitrogen dioxide (NO2)
- Sulfur dioxide (SO2)
- Carbon monoxide (CO).
The concentration values of these pollutants, and sometimes other pollutants, are measured over time and used to calculate the Air Quality local Index. Different countries/regions measure different pollutants for the index definition. For example:
- The European AQI reports on the 5 separate pollutants mentioned above.
- The India AQI reports the pollutants above and on ammonia (NH3).
The Air Quality local Index is influenced by several other factors, such as:
- Wind speed and direction
- Terrain
- Smoke plumes
- Traffic
- Other sources that emit fine particle pollution
Important:
- Pollutant concentrations can be inconsistent over short distances and make air quality readings vary between locations.
- Each monitoring station may not measure every pollutant. This difference can sometimes lead to discrepancies between reported AQI, which are station-specific and reflect only pollutants measured at that station, and actual air quality.
You can learn more about the Air Quality Index in your area with information provided by our partners and third-party sources:
Australia
- Australian Capital Territory Government
- Environment Protection Authority (EPA) Victoria
- Environment Protection Authority (EPA) South Australia
- New South Wales Government
- Northern Territory Environment Protection Authority (EPA)
- Queensland Government
- Government of Western Australia
- Environment Protection Authority (EPA) Tasmania
Brazil
Chile
India
Israel
Mexico
Singapore
South Korea
US
How Air Quality Index (AQI) near you is selected
AQI levels are measured at particular air quality stations and do not necessarily reflect the AQI level at your location. For example, if wind is blowing, upstream stations might be more related to the AQI at your location than closer downstream stations. To avoid confusion, we show a map-based view to display the AQI level at given stations around you.
Due to space constraints, several Google products do present a single-station reading. In that case, the AQI value is selected according to the closest station to your location.
What are the most common types of outdoor pollutants?
The Air Quality local Indexes are based on measurements of air pollutants.
The most commonly measured pollutants outdoors are:
- Particulate matter (PM): Small solid particles and liquid droplets found in the air. PM10 and PM2.5 refers to particles with a diameter smaller than 10 micrometers and 2.5 micrometers, respectively. It’s derived from motor vehicles, wood heaters, and industry. Fires and dust storms can also produce high concentrations of particulate matter.
- Nitrogen dioxide (NO2): A gas and a major component of central city air pollution. It mainly comes from vehicles, industry, power stations, and heating.
- Ozone (O3): A gas composed of 3 atoms of oxygen. Ozone is made by a chemical reaction between the sun’s rays, organic gasses, and oxides of nitrogen released by:
- Cars
- Power plants
- Other sources
- Sulfur dioxide (SO2): A toxic gas, with a pungent, irritating odor. It can come from electric industries that burn fossil fuels, petrol refineries, and cement manufacturing.
- Carbon monoxide (CO): A gas that is derived from motor vehicles or machinery that burn fossil fuels.
What do the smoke plumes mean?
Important: The map might show yesterday’s smoke while today’s smoke is still being analyzed. In some cases, the AQI might be good while there’s a smoke plume. This can be caused in cases where the smoke plume doesn’t reach the ground surface and doesn’t affect the measured air quality.
Additional information about smoke in the US is provided based on satellites’ data from NOAA, available in Google Search and Maps.
The data includes medium and high levels of smoke density. Smoke plumes will be shown on the air quality map if data is available.