Atmosphere And Weather

How is Air Quality Measured

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Air quality is measured by the Air Quality Index, which falls under the jurisdiction of the Environmental Protection Agency (EPA). The EPA, on a daily basis, releases the air quality index (AQI) for that particular day. If air quality is at an unacceptable or dangerous level, the EPA issues appropriate alerts. The AQI is a very necessary air quality assessment indicator, particularly for those suffering from respiratory or other diseases that may be aggravated by poor air quality.

The AQI Measurements and Calculations

The Air Quality Index (AQI) measures five air pollutants, regulated by the Clean Air Act. Those pollutants are particulate matter (smog), carbon dioxide, sulfur dioxide, nitrogen dioxide and ground level ozone levels. Of the five pollutants measured by the AQI, ground level ozone and particulate matter (smog) pose the greatest risks. However, in early June, 2010, the EPA released new national air quality guidelines for sulfur dioxide, mostly released from power and industrial plants. Air quality is monitored at over 1,000 locations throughout the United States on a daily basis. The monitors record pollutant levels which are then plugged into the EPA’s values for each of the 5 pollutants. The measurements are then converted to AQI values. The pollutant with the highest AQI is used as the overall AQI on that day. On the Air Quality Index, the lower the number, which ranges from 0 to 500, the better. When the AQI readings start rising, the poorer the air quality. A reading of 0-50 is ideal. Once the AQI rises to 100 or above, at-risk groups suffer. If the AQI readings continue to rise, more people are likely to suffer adverse effects of air pollution. Once the AQI reaches a reading of 300 or above, air quality is at hazardous levels and high risk groups, as well as others, may need medical treatment. One can view the AQI chart on the EPA website (

AQI Categories

There are various categories and related colors on the EPA’s AQI chart. This breaks down the readings and gives a clear understanding of the Air Quality Index. Green indicates an AQI of 0-50 and is the best reading. 51-100 is designated by yellow. Air quality is still acceptable but particulates may affect some special groups of people. 101-150 is the AQI represented by orange. This air quality rating is unhealthy for those suffering respiratory diseases, and those who have heart disease. Health risks increase to more of the population when the AQI reaches the red level with an AQI reading of 151-200. At this level, adverse health effects can result to the at-risk population. The purple level on the AQI chart is designated for air quality in the 201-300 range. At this level, all people can suffer adverse health effects due to the poor air quality. A health alert would be issued. The highest level is the maroon level with an AQI reading of over 300. At this point the EPA would declare air quality hazardous to the entire population.

How to Find Air Quality Index Readings

The AQI is very readily available to citizens. Most television channels and many radio stations publicize the daily AQI reading. Many newspapers also give the AQI reading. One can also find the daily AQI on the EPA website. The Weather Channel offers air quality information of every state when one visits the website and clicks on the “health” link.

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