Countries around the world measure air quality, both for regulatory and reporting purposes but also to better understand the nature of air pollution and explore potential solutions to mitigate its effects. There are a number of compounds that constitute air pollution, including particulate matter (PM), which is mixture of solid and liquid particles suspended in air, as well as common gases such as NO₂, CO₂ and O₃ to name a few.
As such, different countries have developed their own air quality indices in order to effectively communicate levels of pollution to the public. Each country’s air quality index corresponds to its own national standards. Two well known indices are the Common Air Quality Index (CAQI), which has been used in Europe since 2006, and the Air Quality Index (AQI), which is used by the United States. The purpose of indices like these is to facilitate straightforward comparisons between nations.
The CAQI was born out of a desire to easily compare air quality across the EU and warn citizens of the dangers of exceedingly high levels of pollution. It is a number on a scale from 0 to 100, and the higher the number the worse the air quality is. The index is further divided into both hourly and daily versions, and also separated depending on where measurements are being taken (“roadside” vs “background”). The two mandatory measurements for the “roadside” CAQI are NO₂ and PM10 (particulate matter less than or equal to 10 µm in diameter), with O₃ also required for the “background” index. The five qualitative categories that correspond to the index range from “very low” for values from 0 to 25 to “very high” for values that exceed 100.
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Similar to the CAQI, the AQI was developed by the US to communicate levels of air pollution to the public. It began in 1968, with the methodology being developed ever since then. It is divided into six categories, and is a number on a scale from 0 to 500. In general, levels below 50 represent good air quality while those above 300 are dangerous. More components constitute the AQI than the CAQI, five to be specific: PM, O₃, CO, SO₂, and NO₂. The index is calculated using measured concentrations and established breakpoints of pollutants, with the highest value applied. In locations where multiple pollutants are measured, the most dominant value is reported. The Environmental Protection Agency (EPA) shares the AQI with the public via its dedicated website, AirNow.
In general, levels below 50 represent good air quality.
The index is calculated using measured concentrations and established breakpoints of pollutants, with the highest value applied. In locations where multiple pollutants are measured, the most dominant value is reported.
It means that air quality is very serious for your health and you should not stay outdoors.
Values over 151 are considered unsafe and can cause negative health effects
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