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Air Quality Index AQI Explained How to Breathe Healthier Air
Air Quality Index AQI Explained How to Breathe Healthier Air

Air Quality Index (AQI) it’s a standardized system used to measure and communicate the quality of the air in a specific location. The AQI provides information about how polluted the air is and what potential health effects might be associated with different levels of pollution. EPA and local officials use the AQI to provide simple information about your local air quality, how unhealthy air may affect you, and how you can protect your health. Local air quality affects how you live and breathe, like weather it may change from day to day and even hour to hour. The AQI is an index for reporting daily air quality. It tells us how clean or unhealthy our air is, and what associated health effects might be a concern.

The AQI is calculated for major air pollutants regulated by the Clean Air Act: or policy ground level ozone, particle pollution, carbon monoxide, and sulfur dioxide. For each of these pollutants, EPA has established national air quality standards to protect public health and environment. EPA is currently reviewing their national air quality standard for nitrogen dioxide.

The AQI takes into account several pollutants that can be present in the air, such as:

Particulate Matter (PM2.5 and PM10)

These are tiny particles suspended in the air that can be harmful when inhaled. PM2.5 refers to particles with a diameter of 2.5 micrometers or smaller, while PM10 refers to particles with a diameter of 10 micrometers or smaller. Particle pollution consists mixture of solid and liquids droplets. Its pollution levels can be very unhealthy and even hazardous during events such as forest fires. Particle come in wide range of sizes. Those less than 10 micrometers in diameter (smaller than the width of a single human hair) are so small that they can get into the lungs, where they can cause serious health problems.

Ground-level Ozone (O3)

Ozone at ground level is a result of chemical reactions between pollutants emitted from vehicles, industrial sources, and natural sources. High levels of ozone can be harmful to human health. Its pollution is more likely to form during warmer months. This is when the weather conditions normally needed to form ground-level ozone lots of sun occur.

Nitrogen Dioxide (NO2)

This gas is produced by burning fossil fuels, primarily from vehicles and industrial processes. It can irritate the respiratory system and contribute to the formation of other pollutants, like Nitric acid and ozone by addition of water and sunlight respectively.

Sulfur Dioxide (SO2)

This gas is produced by burning fossil fuels containing sulfur, such as coal and oil. It can lead to respiratory problems and contribute to the formation of particulate matter. Sulfur dioxide, a colorless, reactive gas. Generally, the highest levels of sulfur dioxide are found near large industrial complexes. Major sources include power plants, refineries, and industrial boilers.

Carbon Monoxide (CO)

This colorless, odorless gas is produced by incomplete combustion of carbon-containing fuels. It can interfere with the body's ability to transport oxygen and can be particularly harmful to those with cardiovascular issues. Its levels typically are highest during cold weather, because cold temperatures make combustion less complete and cause inversions that trap pollutants close to the ground.

The AQI scale typically ranges from 0 to 500, with higher values indicating worse air quality. Although an AQI value of 50 represents good air quality with little or no potential to affect public health and environment, while an AQI value over 300 represents air quality so hazardous that everyone may experience serious health effects. An AQI value of 100 generally corresponds to the national air quality standard for the pollutant, which is the level EPA has set to protect public health. AQI values at or below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is considered to be unhealthy—at first for certain sensitive groups of people, then for everyone as AQI values increase.

The scale is divided into several categories, each corresponding to a different level of health concern:

0-50: Good (Green) -

Air quality is considered satisfactory, and air pollution poses little or no risk.

51-100: Moderate (Yellow)

Air quality is acceptable; however, there might be a moderate health concern for a very small number of people or sensitive group, who are unusually sensitive to air pollution.

101-150: Unhealthy for Sensitive Groups (Orange)

Members of sensitive groups, such as children, the elderly, and individuals with respiratory or heart conditions, may experience health effects. The general public is not likely to be affected.

151-200: Unhealthy (Red)

Everyone may begin to experience health effects, and members of sensitive groups may experience more serious effects on their health.

201-300: Very Unhealthy (Purple) - Health alert

everyone may experience more serious health effects.

301-500: Hazardous (Maroon)

Health warnings of emergency conditions. The entire population is more likely to be affected.

The measurements of each pollutants are converted into a separate AQI value for (ground-level ozone, particle pollution, carbon monoxide, and sulfur dioxide) using standard formulas developed by EPA. The highest of these AQI values is reported as the AQI value for that day. When the AQI is above 100, agencies must also report which groups, such as children or people with asthma or heart disease, may be sensitive to that pollutant. If two or more pollutants have AQI values above 100 on a given day, agencies must report all the groups that are sensitive to those pollutants. For example, if a community’s AQI is 130 for ozone and 101 for particle pollution, the AQI value for that day would be announced as 130 for ozone. The announcements would note that particle pollution levels were also high and would alert groups sensitive to ozone or particle pollution about how to protect their health. Many cities also provide forecasts for the next day’s AQI. These forecasts help local residents protect their health by alerting them to plan their strenuous outdoor activities for a time when air quality is better.

AQI values are calculated based on real-time measurements of pollutant concentrations and are used by government agencies, environmental organizations, and the public to make informed decisions about outdoor activities and protective measures during periods of poor air quality.

How Can I Find AQI

You can AQI of your cities by Sign up for EnviroFlash (www.enviroflash.info), a free service that will alert you via e-mail when air quality is forecast to be

Formula for Measuring AQI

The Air Quality Index (AQI) is calculated based on the concentrations of specific air pollutants. The formula for AQI varies depending on the pollutant of concern, such as particulate matter (PM2.5 or PM10), ozone (O3), sulfur dioxide (SO2), nitrogen dioxide (NO2), and carbon monoxide (CO).

AQI formula and breakpoints for calculating the AQI for particulate matter (PM2.5) according to the United States Environmental Protection Agency (EPA) standard:Measure the concentration of PM2.5 in µg/m³.Determine the AQI values for different concentration ranges:

Good: 0 - 12.0 µg/m³

Moderate: 12.1 - 35.4 µg/m³

Unhealthy for Sensitive Groups: 35.5 - 55.4 µg/m³

Unhealthy: 55.5 - 150.4 µg/m³

Very Unhealthy: 150.5 - 250.4 µg/m³

Hazardous: 250.5 - 500.4 µg/m³

Calculate the AQI using the following formula

AQI = [(AQI value for higher concentration range - AQI value for lower concentration range) / (Higher concentration range - Lower concentration range)] * (Measured concentration - Lower concentration range) + AQI value for lower concentration range

For example, let's say you have a PM2.5 concentration of 25 µg/m³:

AQI = [(50 - 35) / (35.4 - 12.1)] * (25 - 12.1) + 35

AQI = 68 (approximately)

This would put the AQI value of 68 in the "Moderate" category.Keep in mind that AQI formulas and breakpoints can vary based on different standards and guidelines used by different countries or organizations. This example is based on the US EPA standard.

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