Air pollution, or smog as it is commonly referred to, is a mixture of several gases, water vapor and small, solid particles. Smog is caused by automobile emissions, factories, farming, coal burning and fires. Even natural disasters, such as volcanic eruptions, can release enormous amounts of dust and smoke into the atmosphere that can travel for thousands of miles. Common pollutants include soot, dust, smoke and aerosols, as well as:
- Ozone - a colorless, odorless gas that is formed from the combination of heat, sunlight and various chemicals that are emitted from automobiles and industry. This pollutant has been found to cause breathing problems, eye irritation and nausea. Long-term effects of ozone on lung function currently are being studied.
- Carbon monoxide - a colorless, odorless gas produced from automobile exhaust. It lowers the amount of oxygen in the blood, which ultimately limits the amount of oxygen that is transported to working muscles.
- Sulphur dioxide - a primary respiratory pollutant produced from burning coal that can cause breathing difficulties, especially in people with asthma.
- Suspended particles - solid matter in the form of smoke, dust and vapor that is produced from diesel exhausts, wood burning, fires and farming, etc. Particle pollution can irritate the lungs and even has been linked to premature deaths from heart and lung ailments.
Clearly, air pollutants can cause complications for outdoor exercisers, depending upon the types and levels of pollutants and individual susceptibility. At rest, an average person breathes approximately 600 liters of air/hour. Exercise ventilations can reach in excess of 7,000 liters/hour. Thus, any pollutants in the ambient air are likely to be inhaled and come into contact with lung tissue and other tissues, such as those in the cardiovascular system.
The main problem with air pollutants is that they are inhaled. Nasal breathing has been found to prevent some pollutants from reaching deeper into the lungs. During exercise, however, nasal breathing is limited; most exercisers breathe through their mouth. Because air filtration is much less efficient with mouth breathing, more pollutants are able to reach the lungs.
Although some pollutants are highly visible, such as particulate matter, many (such as carbon monoxide and ozone) are invisible and cannot be detected by any of our senses. So it is prudent to understand when and where pollutants are present and avoid the times and locations where they occur. Pollutants usually are concentrated in urban areas but are not limited to them.
Furthermore, air pollutants can travel long distances and often concentrate in specific areas, according to winds and geography. For example, in southern California, winds usually blow from west to east, so pollutants such as ozone are carried to the eastern area of the state where mountains act as a sort of a basin to keep the pollutants concentrated here.
Because ozone requires heat and sunlight for its formation, the worst time it is present in the United States typically is from May to September. In addition, late afternoons are usually peak times. Thus, when exercising during summer months in the U.S., it is smart to restrict activities to early morning or late evening.
Carbon monoxide, on the other hand, is usually highest directly at the source - vehicular emissions. Therefore, it is not recommended to exercise during or near heavy traffic.
The presence of more than one pollutant - which often happens with smog - can more powerfully affect the body as well. Also, other environmental factors such as heat, cold and altitude, combined with air pollutants, can have an additive effect on breathing.
Immediate symptoms of breathing noxious pollutants include coughing, chest pain, wheezing and reduced breathing ability. Long term exposure is believed to cause chronic lung and heart diseases and reduce immunity to diseases.
WHO IS SUSCEPTIBLE?People who are most susceptible to air pollutants include children, elderly, asthmatics and those with heart or lung disease. Also, some people have allergic reactions to dust or specific chemicals.
Children often are active outdoors during the times when ozone might be at its peak. If you are exercising where there is moderate air pollution, it is recommended to reduce the intensity of exercise to decrease the volume of ventilated air. Exercising indoors during episodes of severe pollution is the safest option.
Individuals who are active outdoors should be aware of the types of pollutants prevalent in their area. Reports of air quality are usually listed in most local newspapers or are available through meteorologists. In addition, the U.S. Environmental Protection Agency (EPA) at www.epa.gov is an excellent source of information on air quality locally and nationally.
The following tips are helpful to keep in mind when exercising outdoors as well:
- Avoid exercise during rush hours.
- Avoid cigarette smoking areas prior to and during exercise.
- Avoid combinations of high temperature, humidity and air pollution.
- Limit the amount of time spent in high pollution areas.
Certainly, exercise is very beneficial - indoors or out - and people should be careful to take precautions when necessary to exercise safely outdoors in a polluted environment.
# # #Robert Girandola, Ph.D., is a professor in the Department of Kinesiology at the University of Southern California in Los Angeles, Calif.
