Air Pollution Action Day
Air Quality Index
A Guide to Air Quality and Your Health
Introduction
Increasingly, radio, TV, and newspapers are providing information like this to local communities. But what does it mean to you ...if you are planning outdoor activities that day? ...if you have children who play outdoors? ...if you are an older adult? ...if you have asthma? This booklet will help you understand what you can do to protect yourself from air pollution.
Local air quality affects how you live and breathe. Like the weather, it can change from day to day or even hour to hour. The U.S. Environmental Protection Agency (EPA) and others are working to make information about outdoor air quality as easy to understand as the weather forecast. A key tool in this effort is the Air Quality Index, or AQI. EPA and local officials use the AQI to provide you with simple information on local air quality, the health concerns for different levels of air pollution, and how you can protect your health when pollutants reach unhealthy levels.
What is the AQI?
The AQI is an index for reporting daily air quality. It tells you how clean or polluted your air is, and what associated health effects might be a concern for you. The AQI focuses on health effects you may experience within a few hours or days after breathing polluted air. EPA calculates the AQI for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide. For each of these pollutants, EPA has established national air quality standards to protect public health.
Back to contentsHow does the AQI work?
Think of the AQI as a yardstick that runs from 0 to 500. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 represents good air quality with little potential to affect public health, while an AQI value over 300 represents hazardous air quality.
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 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 get higher.
Back to contentsUnderstanding the AQI
The purpose of the AQI is to help you understand what local air quality means to your health. To make it easier to understand, the AQI is divided into six categories:
| Air Quality Index (AQI) Values |
Levels of Health Concern | Colors |
|---|---|---|
| When the AQI is in this range: |
...air quality conditions are: | ...as symbolized by this color: |
| 0 to 50 | Good | Green |
| 51 to 100 | Moderate | Yellow |
| 101 to 150 | Unhealthy for Sensitive Groups |
Orange |
| 151 to 200 | Unhealthy | Red |
| 201 to 300 | Very Unhealthy | Purple |
| 301 to 500 | Hazardous | Maroon |
Each category corresponds to a different level of health concern. The six levels of health concern and what they mean are:
- "Good"
The AQI value for your community is between 0 and 50. Air quality is
considered satisfactory, and air pollution poses little or no risk.
- "Moderate"
The AQI for your community is between 51 and 100. Air quality is
acceptable; however, for some pollutants there may be a moderate health
concern for a very small number of people. For example, people who are
unusually sensitive to ozone may experience respiratory symptoms.
- "Unhealthy for Sensitive Groups"
When AQI values are between 101 and 150, members of sensitive groups
may experience health effects. This means they are likely to be
affected at lower levels than the general public. For example, people
with lung disease are at greater risk from exposure to ozone, while
people with either lung disease or heart disease are at greater risk
from exposure to particle pollution. The general public is not likely
to be affected when the AQI is in this range.
- "Unhealthy"
Everyone may begin to experience health effects when AQI values are
between 151 and 200. Members of sensitive groups may experience more
serious health effects.
- "Very Unhealthy" AQI values between 201 and 300 trigger a health alert, meaning everyone may experience more serious health effects.
- "Hazardous" AQI values over 300 trigger health warnings of emergency conditions. The entire population is more likely to be affected.
AQI colors
A specific color is assigned to each AQI category to make it easier for you to understand quickly whether air pollution is reaching unhealthy levels in your community. For example, the color orange means that conditions are "unhealthy for sensitive groups," while red means that conditions may be "unhealthy for everyone," and so on.
Back to contentsHow is a community's AQI calculated?
Air quality is measured by monitors that record the concentrations of the major pollutants each day at more than a thousand locations across the country. These raw measurements are then converted into AQI values using standard formulas developed by EPA. An AQI value is calculated for each pollutant in an area (ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide). The highest AQI value for the individual pollutants is the AQI value for that day. For example, if on July 12 a certain area had AQI values of 90 for ozone and 88 for sulfur dioxide, the AQI value would be 90 for the pollutant ozone on that day.
Back to contentsWhen and how is the AQI reported to the public?
In large cities (more than 350,000 people), state and local agencies are required to report the AQI to the public daily. 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 the specific 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. Many smaller communities also report the AQI as a public health service.
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 activities for a time when air quality is better.
The AQI is a national index, so the values and colors used to show local air quality and the levels of health concern will be the same everywhere you go in the United States. Look for the AQI to be reported in your local newspaper, on television and radio, on the Internet, and on many state and local telephone hotlines.
- AQI in the Newspaper
Newspapers in many U.S. cities, and some national newspapers, carry AQI reports each day. Here is one example: - AQI in Television and Radio Weather Reports
Many local television or radio weathercasters use the AQI to provide air quality information in your area. Here's the type of report you might hear: - AQI on the Internet
EPA's AIRNow web site (www.epa.gov/airnow) contains general information about air pollution plus real-time and forecast air quality data. It also contains facts about the health and environmental effects of air pollution, steps you can take to protect your health and to reduce pollution, and links to state and local air pollution agency web sites.
| Tomorrow will be a code red air quality day for Center City. The cold winter air, morning traffic, and wood smoke are expected to cause particle pollution to rise to unhealthy levels. People with heart or lung disease, older adults, and children should avoid strenuous activities. |
