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Our Air Quality

Facts About Air Pollution

To reduce air pollution, it helps to understand what it is and where it comes from. Here are some facts about air pollution and its most common types in Maricopa County.


What is ozone? Ozone is a colorless gas made up of three oxygen atoms (or O3). This gas is a powerful chemical that causes damage to rubber, plastics, and vegetation. It also irritates people’s eyes, nose, throat, and respiratory system when they are exposed to it. Permanent lung damage also occurs.

The Good

Stratospheric ozone forms high in the atmosphere (six to 30 miles above the Earth) when intense sunlight causes oxygen molecules (O2) to break up and re-form as ozone molecules (O3). Popularly called “good ozone,” it shields people, trees, crops, property, and microorganisms from the harmful effects of the sun’s ultraviolet light (UV-B radiation) because it adsorbs UV radiation before it can get to the earth’s surface (this radiation causes sunburns and skin cancer).

The Bad

Ground-level ozone is often called “bad ozone.” This pollutant forms at ground level when nitrogen oxides (NOx) and volatile organic compounds (VOCs) chemically react under the influence of heat and sunlight. Examples of VOCs are vapors of gasoline, alcohol, paint thinner, and many solvents. The sources of the NOx and VOCs are motor vehicles, industrial operations such as paint shops, manufacturing, and energy production. Some VOCs even come from vegetation. Because of the nature of its formation, ozone is also known as photochemical smog. It is a pollutant of great concern because it harms people when they are exposed to it. Although it is invisible, it causes eye, nose, throat and lung irritation along with permanent lung damage (scarring and decreased lung function) as we breathe it in.

The Ugly

One of the unfortunate facts about air pollution is that ground-level ozone is a man-made phenomenon. It would not be a problem for humankind if there were only natural sources emitting VOCs (plants) and NOx (wildfires) because very little ozone would form at ground-level. However, man-made emissions have resulted in ground-level ozone becoming the most wide-spread air quality problem in the United States. It is most severe in the summer months when there is plenty of heat and sunlight to cook trapped pollutants into ground-level ozone.


What Are They?

Particulate pollution (PM-10 and PM-2.5) is made up of tiny particles  of solid or liquid droplets containing smoke, dust, ash and condensed vapors introduced into the air through natural and man-made causes. It occurs year-round, but is dominant during winter months. Smaller than a human hair, it passes through the throat and nose and enters the lungs, and can lead to health problems.

One Serious Pollutant

Maricopa County and the U.S. Environmental Protection Agency have designated six criteria pollutants, Particulate matter being the Valley’s toughest to battle. Here they are:

  • Particulate matter: very small solid or liquid droplets such as dust, dirt, soot or smoke from wood-burning fires.
  • Ozone: a colorless and mostly odorless gas that is a natural and beneficial component of the upper atmosphere. At ground level, ozone is a respiratory irritant that forms from a photochemical reaction from sunlight reacting with fumes from fuel, paint, cleaners, tailpipes and vegetation. Ozone pollution is typically worse in summer.
  • Carbon Monoxide: a colorless, odorless gas that results primarily from combustion in cars and trucks.
  • Nitrogen Dioxide: a reddish brown gas formed as a byproduct of fuel combustion.
  • Sulfur Dioxide: a colorless gas with a pungent odor produced from the smelting of copper oxide ore, and also from burning sulfur-containing gasoline and diesel fuel.
  • Lead: once a gasoline additive which resulted in high lead air pollution levels, this element is no longer found in gasoline within the United States.

The Maricopa County Air Quality Department monitors for these criteria pollutants.  Its Air Monitoring Division offers enhanced data from the monitoring network including:

  • Real-time updates for PM-10
  • Hourly updates for remaining criteria pollutants
  • Real-time meteorology
  • National Weather Service radar
  • Satellite imagery
  • Air Quality Index ratings