The Air Quality Index (AQI) has six categories of air quality and these include, Good, Satisfactory, Moderately polluted, poor, very poor, and severe.
As with changes in weather from day to day or even hour to hour, the quality of outdoor air also always changes and affects healthy lives.
Therefore, it is very much necessary to monitor the quality of outdoor air and awareness of daily levels of air pollution, especially for those suffering from illnesses caused by exposure to air pollution. The outdoor air quality is monitored by a key tool called as air quality index (AQI).
The AQI focuses on health effects the public may experience within a short time period (a few hours or days) after breathing polluted air. When AQI increases, the health risk to the public also increases.
Therefore, the main purpose of the air quality index is to help people know how the local air quality impacts their health. Corresponding to different national air quality standards, different countries have their own air quality indices.
According to the United States, Environmental Protection Agency (EPA) AQI is divided into six categories indicating increasing levels of health concern.
History of Air Quality Index (AQI)
When was the air quality index introduced?
The AQI came to public knowledge in 1968 when the National Air Pollution Control Administration of the United States Environmental Protection Agency (EPA) undertook an initiative to develop an air quality index and to apply the methodology to Metropolitan Statistical Areas (a geographical region with a relatively high population density at its core and close economic ties throughout the area).
The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters.The EPA has its headquarters in Washington, D.C. . It conducts environmental assessment, research, and education and has the responsibility of maintaining and enforcing national standards under a variety of environmental laws, by consulting with state, tribal, and local governments.
How does the AQI work? | How is AQI calculated?
The value of AQI ranges from 0 to 500. The public health concern is directly proportional to the AQI value. The higher the AQI value, the greater the level of air pollution and the greater the health concern.For example, an AQI value over 300 represents hazardous air quality and below 50 the air quality is good for health.
The EPA established an AQI for five major air pollutants regulated by the Clean Air Act. Each of these pollutants has a national air quality standard set by EPA to protect public health.According to EPA, these five major air pollutants include; 1. Ground-level ozone (O3), 2. Particle pollution/particulate matter (PM2.5/PM10), 3. Carbon Monoxide (CO), 4. Sulfur dioxide (SO2), and 5. Nitrogen dioxide (NO2).
For each pollutant, an AQI value of 100 generally corresponds to an ambient air concentration. The AQI values at or below 100 are generally thought of as satisfactory.When AQI values are above 100, air quality is unhealthy: at first for certain sensitive groups of people, then for everyone as AQI values get higher.
The AQI has six categories of air quality and these include, Good, Satisfactory, Moderately polluted, poor, very poor, and severe. Each category has a specific color and corresponds to a different level of health concern.The color makes it easy for people to remember and quickly determine the quality of air, whether the quality of air in their communities is reaching unhealthy levels so that they could aware of outdoor air quality.The concept of AQI has been widely used in many developed countries over the last three decades.
|AQI value||AQI Categories||Level of Health Impacts|
|51–100||Satisfactory||May cause minor breathing difficulties in sensitive people|
|101–151||Moderately Polluted||May cause breathing difficulties in people with lung disease like asthma, &|
discomfort to people with heart disease, children, and older adults.
|201–300||Poor||May cause breathing difficulties in people on prolonged exposure, and|
discomfort to people with heart disease
|301–400||Very Poor||May cause respiratory illness in people on prolonged exposure.|
The effect may be more pronounced in people with lung and heart diseases.
|401-500||Severe||May cause respiratory issues in healthy people, and serious health issues in|
people with lung/heart disease.
Difficulties may be experienced even during light physical activity.
Table of Air Quality Index values, categories, and health impacts
Objectives of Air Quality Index (AQI)
- Comparing air quality conditions at different locations/cities.
- It also helps in identifying faulty standards and inadequate monitoring programs.
- AQI helps in analyzing the change in air quality (improvement or degradation).
- AQI informs the public about environmental conditions. It is especially useful for people suffering from illnesses aggravated or caused by air pollution.
Causes of poor air quality
There are many factors responsible for poor air quality. Air pollution of the specific area comes from both local pollutant emissions from sources such as industries, cars, and homes, as well as pollution that is blown into that specific area from surrounding areas.
A short-term increase in pollution emissions of a specific area is not responsible for the poorest air quality days (notable exceptions include fireworks or wildfire smoke).Rather, most poor air quality days are driven by changing weather conditions that increase the rate at which air pollutants are formed or accumulate in the air.
Ozone pollution is not directly emitted from emission sources. The ozone pollution levels increase on very hot and sunny days with little wind. Ozone pollution is formed through a chemical reaction between emitted nitrogen oxides and volatile organic compounds in the atmosphere.This reaction is sped up by the hot and sunny weather and causes an increase in ozone pollution levels.
Fine particle pollution
The pollution due to fine particles can be elevated at any time of the year. Fine particles are microscopic pollutants that are easily trapped in the air and are emitted directly from pollution sources.These fine particles are produced due to the reactions between emitted sulfur oxides, nitrogen oxides, and ammonia in the air.
Weather conditions, such as high pressure, high humidity, strong overnight temperature inversions, or low wind speeds can cause an increase in fine particle pollution.
The air pollution levels vary and depend on the year-to-year variations in meteorological patterns in an area.
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FAQ related to air quality index
Who created the air quality index?
U.S. Environmental Protection Agency (EPA)
Where is the best air quality in the world?
Here are the top five major cities with the cleanest air in the world:
Auckland, New Zealand.
What country has the worst air quality?
Bangladesh (US AQI- 162)
Which city in India is the most polluted city?
Bhiwadi, Rajasthan (US AQI – 195)
What are the symptoms of poor air quality?
Dryness and irritation of the eyes, nose, throat, and skin.
Shortness of breath.
Hypersensitivity and allergies.
Coughing and sneezing.
Is there an app to check air quality?
EPA’s AirNow mobile app provides a simple interface for quickly checking current and forecast air quality information for planning daily activities and protecting your health.