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A program of the American Lung Association of the Southeast

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What Is Air Pollution?


Air pollution is a variety of substances and gases in our air that pose risks to health.

Important air pollutants include ozone, nitrogen oxides (NOx), sulfur dioxide (SO2), particulate matter (PM), volatile organic compounds (VOCs), toxic substances such as mercury and some naturally occurring substances such as pollen.

What is Smog or Ozone?

Ozone can be good or bad depending on where it is located. Ozone in the stratosphere high above Earth protects human health and the environment, but ground-level ozone is a serious health concern. Ozone is produced by a combination of two kinds of compounds, nitrogen oxides (NOx) and volatile organic compounds (VOCs). VOCs are produced by both natural and human processes, but NOx come primarily from fossil fuel combustion — cars, trucks, diesel equipment, power plants and industry. These smog-forming pollutants react with one another in the atmosphere in the presence of intense sunlight to form ground-level ozone.

What is Soot or Particulate Matter?

Particles found in the air, including dust, dirt, soot, smoke and liquid droplets, are known as particulate matter (PM). Particles can be suspended in the air for long periods of time. Some particles are large or dark enough to be seen as soot or smoke, while others are so small that they can only be detected with an electron microscope.

Some particles are directly emitted into the air and come from a variety of sources such as cars, trucks, buses, factories, construction sites, tilled fields, unpaved roads and wood burning. Other kinds of particles are formed in the air when gases from burning fuels react with other compounds in the atmosphere.

These particles can get trapped in the lungs and cause pulmonary and circulatory problems, as well as trigger asthma attacks.

High levels of PM have also been linked to Sudden Infant Death Syndrome (SIDS) and slow lung function growth in children.

Read more about how exposure to particulate matter and ozone exacerbates respiratory and cardiovascular diseases.