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Air Quality Contaminants

Ozone

Ozone is a gas that you cannot see or smell. Ozone occurs naturally in the sky about 10 to 30 miles above the earth's surface. Sometimes, this ozone is called “good ozone” because it forms a layer that protects life on earth from the sun's harmful rays.

Ground-level ozone, on the other hand, can be bad for your health and the environment. Ground-level ozone forms when pollutants from cars and trucks, power plants, factories, and other sources come in contact with each other in heat and sunlight. Factors such as weather conditions and intensity of sunlight also play a part in how ozone is formed. Ground-level ozone is one of the biggest parts of smog, and it is usually worse in the summer months.

Many urban areas tend to have higher levels of ground-level ozone. However, rural areas have ground-level ozone, too. Wind carries ozone and the pollutants that form it hundreds of miles from their original sources, and rural areas have sources of ozone that contribute to this problem.

Particulate Matter

Particle pollution, or particulate matter, consists of particles that are in the air, including dust, dirt, soot and smoke, and little drops of liquid. Some particles, such as soot or smoke, are large or dark enough to be seen. Other particles are so small that you cannot see them.

Particle pollution can come from primary or secondary sources. A primary source, such as wood stoves or forest fires, lets off particle pollution directly. A secondary source lets off gases that react and form particles. Examples of secondary sources are coal fires and power plants. Particle pollution also comes from motor vehicles, factories, and construction sites. These can be primary or secondary sources. Particle pollution can be a problem at different times of the year, depending on where you live.

Particle pollution includes:

  • coarse particles that are between 2.5 and 10 micrometers,
  • fine particles that are between 0.1 micrometers and 2.5 micrometers; also known as PM2.5, and
  • ultrafine particles that are smaller than 0.1 micrometers.

Particles bigger than 10 micrometers can irritate your eyes, nose, and throat but do not usually reach your lungs. Ten micrometers is about seven times thinner than one human hair.

Fine and ultrafine particles are the most concerning because they are most likely to cause health problems. Their small size allows them to get into the deep part of your lungs and even into your blood.

Data and information for this site are still being developed and added.  We welcome your comments and feedback.

This effort is supported by funding from the U.S. Centers for Disease Control and Prevention Environmental Public Health Tracking Program, Cooperative Agreement Number 5U38EH000619-02. The contents of this Website are solely the responsibility of the authors and do not necessarily represent the official views of the Centers for Disease Control and Prevention.