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. Ground-level ozone and particle pollution are the two pollutants that pose the greatest threat to human health in this country.
Ozone is a gas composed of three atoms of oxygen. Ozone occurs both in the Earth's upper atmosphere and at ground level. Ozone can be good or bad, depending on where it is found: Good Ozone: Ozone occurs naturally in the Earth's upper atmosphere - 6 to 30 miles above the Earth's surface - where it forms a protective layer that shields us from the sun's harmful ultraviolet rays. Manmade chemicals are known to destroy this beneficial ozone. An area where the protective "ozone layer" has been significantly depleted-for example, over the North or South pole-is sometimes called "the ozone hole.” The United States, along with over 180 other countries, recognized the threats posed by ozone depletion and in 1987 adopted a treaty called the Montreal Protocol to phase out the production and use of ozone-depleting substances. EPA has established regulations to phase out ozone-depleting chemicals in the United States. Bad Ozone: In the Earth's lower atmosphere, near ground level, ozone is formed when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources react chemically in the presence of sunlight. Ozone at ground level is a harmful air pollutant.
Particle pollution — also called particulate matter (PM) — is made up of particles (tiny pieces) of solid or liquid that are in the air. These particles may include:
Some particles are big enough (or appear dark enough) to see — for example, you can often see smoke in the air. Others are so small that you can't see them in the air.
Particle pollution can come from two different kinds of sources — primary or secondary. Primary sources cause particle pollution on their own. For example, wood stoves and forest fires are primary sources.
Secondary sources let off gases that can form particles. Power plants and coal fires are examples of secondary sources. Some other common sources of particle pollution can be either primary or secondary — for example, factories, cars and trucks, and construction sites.
Smoke from fires and emissions (releases) from power plants, industrial facilities, and cars and trucks contain PM2.5. Particle Pollution and Your Health Breathing in particle pollution can be harmful to your health. Coarse (bigger) particles, called PM10, can irritate your eyes, nose, and throat. Dust from roads, farms, dry riverbeds, construction sites, and mines are types of PM10. Fine (smaller) particles, called PM2.5, are more dangerous because they can get into the deep parts of your lungs — or even into your blood.
Particle pollution can affect anyone, but it bothers some people more than others. People most likely to experience health prolems caused by particle pollution includes:
Read more about the health impacts of PM. If you have asthma, particle pollution can make your symptoms worse. Carefully follow your asthma management plan on days when pollution levels are high.
If you have heart disease, breathing in particle pollution can cause serious problems like a heart attack. Symptoms include:
If you have any of these signs, contact your doctor. Be sure to let your doctor know if the symptoms get worse or last longer than usual.
The good news is there's a lot you can do to protect yourself and your family from the health effects caused by particle pollution. Start by learning about the Air Quality Index from the U.S. Environmental Protection Agency (EPA).
The EPA Air Quality Index (AQI) tells you when air pollution is likely to reach levels that could be harmful. You can use the AQI as a tool to help you avoid particle pollution. Local TV stations, radio programs, and newspapers report the AQI. Try checking it when you're planning your daily activities.
When particle pollution levels are high, take steps to limit the amount of air you breathe in while you're outside. For example:Think about spending more time indoors, where particle pollution levels are usually lower. Choose easier outdoor activities (like walking instead of running) so you don't breathe as hard. Avoid busy roads and highways where PM is usually worse because of emissions from vehicles.
The term fine particles, or particulate matter 2.5 (PM2.5), refers to tiny particles or droplets in the air that are two and one half microns or less in width. Like inches, meters and miles, a micron is a unit of measurement for distance. There are about 25,000 microns in an inch. The widths of the larger particles in the PM2.5 size range would be about thirty times smaller than that of a human hair. The smaller particles are so small that several thousand of them could fit on the period at the end of this sentence.
Particles in the PM2.5 size range are able to travel deeply into the respiratory tract, reaching the lungs. Exposure to fine particles can cause short-term health effects such as eye, nose, throat and lung irritation, coughing, sneezing, runny nose and shortness of breath. Exposure to fine particles can also affect lung function and worsen medical conditions such as asthma and heart disease. Scientific studies have linked increases in daily PM2.5 exposure with increased respiratory and cardiovascular hospital admissions, emergency department visits and deaths. Studies also suggest that long term exposure to fine particulate matter may be associated with increased rates of chronic bronchitis, reduced lung function and increased mortality from lung cancer and heart disease. People with breathing and heart problems, children and the elderly may be particularly sensitive to PM2.5.