Both indoor and outdoor pollutants contain chemicals known to be harmful to human health when inhaled. Some of these chemicals include:

• Perchloroethylene, used in dry cleaning
  
  
• Methylene chloride, used in degreasers and consumer products such as paint strippers
  
  
• Benzene, used in gasoline and released when drivers fill their tanks or drive their cars
  
  
• Chromium, used in metal plating operations

The U.S. Environmental Protection Agency (EPA) has identified five pollutants that it considers to be particularly dangerous to human health. They include:

• “Bad” ozone. A mixture of oxygen, nitrogen, oxide gases and volatile organic compounds. It forms when sunlight and heat mixes with vapors and gases from fuel combustion, such as from car exhaust, power plants and other sources. This mixture combines with oxygen to create “bad” ozone. This is different from ozone in the upper atmosphere, which protects the Earth from ultraviolet light. This “good” ozone forms when ultraviolet light from the sun splits an oxygen molecule and forms two single oxygen atoms. These each bind to an oxygen molecule to form ozone.
  
  Ground-level ozone is potentially harmful. Ozone sears the cell walls in the lungs and airway, causing them to become reddened and swollen. Some scientists have referred to it as sunburn on the lining of the lung. The resulting damage:
  
  
• • Impairs lung function and can permanently damage the lungs
    
    
  • Can make health conditions such as asthma and allergies worse
    
    
  • May reduce the body’s ability to fight off bacterial infections

   

  According to the American Lung Association (ALA), nearly one-third of the U.S. population lives in an area with unsafe levels of ozone. High ozone levels account for almost all of the unhealthy air days nationwide.

• Particle pollution. Occurs when tiny particles enter the air from power plant emissions, diesel exhaust, wood burning and other sources. People can easily inhale these microscopic particles, which then penetrate the body’s defense system. Particle pollution has been linked to increased asthma, heart attacks, strokes, lung cancer and reduced life expectancy. According to the ALA, about one-third of the American population lives with unsafe short-term levels of particle pollution, and about 20 percent have unsafe year-round levels.
  
  
• Carbon monoxide. An odorless gas that reduces the oxygen-carrying capability of blood. It is the byproduct of indoor fuel-burning appliances such as gas stoves, gas or oil furnaces, fireplaces, wood stoves, and unvented kerosene or gas space heaters. Other combustion sources that create carbon monoxide include burning charcoal, gasoline engines running inside garages or sheds, unvented kerosene heaters and tobacco smoke.
  
  
• Nitrogen dioxide. An odorless gas that causes bronchial hyperresponsiveness (an exaggerated airway response). It is the byproduct of many of the same products that creat carbon monoxide, including indoor fuel-burning appliances such as gas stoves, gas or oil furnaces, fireplaces, wood stoves, and unvented kerosene or gas space heaters.
  
  
• Sulfur dioxide. A colorless gas with a pungent odor that can reduce lung capacity when inhaled over long periods of time. It is the byproduct of burning coal and oil at power plants and from copper smelting.