Pollution can trigger symptoms of many respiratory disorders, including asthma and allergies. The sources of pollutants are part of the fabric of everyday life and can be found both indoors and outdoors. Major environmental pollutants are released from:

• Chemical plants
• Steel mills
• Oil refineries
• Hazardous waste incinerators
• Automobiles, buses, airplanes and trains
• Dry cleaners
• Small metal plating operations
• Gas stations
• Crop fires and forest fires

Smoke stacks, equipment leaks or failures, explosions and accidents all release pollutants into the atmosphere. The concentration of a pollutant tends to be highest near the source of the pollution, and lower further away as the pollutant is dispersed and spread out through the air. Weather conditions – particularly wind speed and direction – also have a major impact on pollution concentration levels.

Many other pollutants are found not in the environment at large, but indoors in the home or workplace. Some of these pollutants seep in from outside, but others are generated inside the home. These include:

• Tobacco smoke. Secondhand smoke consists of smoke expelled out into the air by a smoker, as well as sidestream smoke produced by the burning end of a cigarette, cigar or pipe.
  
  
• Heating and air conditioning equipment (including wood stoves).
  
  
• Household cleaning products and personal care products. Ingredients that are potentially harmful include potassium hydroxide, perchloroethylene, methylene chloride, mercury, paradichlorobenzene and lead arsenate.
  
  
• Chemicals (e.g., formaldehyde, asbestos) released from construction and remodeling products, such as carpets, paneling and insulation.
  
  
• Radon, a gas from soil around the house that contains uranium. It enters the home through openings or cracks in the foundation floors, walls, drains or joints.

According to an American Lung Association (ALA) annual study, more than half of all Americans are living in counties that have unsafe levels of ozone or particle pollution. These pollutants place them at risk for decreased lung function, respiratory infection, lung inflammation and aggravation of respiratory illness.

Although pollutants have adverse effects on all people, certain people are at higher risk of problems from pollution exposure. They include:

• People with chronic lung disease such as asthma or chronic obstructive pulmonary disease (COPD)
• Children
• Seniors
• People with heart disease
• People with diabetes

Recent studies also indicate that air pollution may hamper lung development in children, possibly by keeping the lungs chronically inflamed and retarding the growth of the lungs’ air sacs (alveoli). Because the lungs stop growing by age 18 and lung capacity gradually declines thereafter, stunted growth can have lifelong consequences.