In the U.S., aid quality is measured by the PSI (Pollutant Standards Index), using a scale of 0 to 500. When the PSI exceeds 100, at least one of the six measured pollutants is higher than federal standards. The six measured pollutants are: ozone (O3), nitrogen dioxide (NO2), carbon monoxide (CO), particulate matter (PM10), sulfur dioxide (SO2), and lead.

Pollution can worsen many medical problems: in the young and old who suffer from lung disease, asthma, chronic obstructive lung disease, lung cancer, and coronary artery disease. Infant and adult mortality have been shown to increase by 5 to 25% when pollution levels are high. When serious health problems occur during heavy pollution, PM-10 and ozone tend to be the major offenders.

Advice For Patients
- Avoid exercising in traffic-congested areas, in the late morning or early evening when the PSI exceeds 100.
- When the PSI is greater than 100, indoor play and exercise should be encouraged for children, older people, pregnant women, anyone with asthma or cardiopulmonary problems.

Ozone (03)
Ground-level ozone is the principal component of smog. In the stratosphere, ozone decreases the amount of ultraviolet (UV) light reaching the earth, but near the ground, ozone can damage health.

Formed in chemical reactions of volatile organic compounds with nitrous oxides. A noxious concoction of ground level sources - from cars, lawn mowers, barbecue grills, smokestacks, oil-based paint fumes, and even bakeries - cooked by heat and sunlight to make ozone. Exposure is highest in LA, Houston, Chicago, and along the East Coast from Maine to Virginia.

Exposure, even in low concentrations can cause eye irritation, chest pain, shortness of breath, cough, and changes in pulmonary function tests.

The Maryland Department of Environment declares a "Code Red" air-quality alert whenever ozone reaches 125 parts per billion for an hour.

Nitrogen dioxide (NO2)
Yellow-brown, water-soluble gas; a major contributor to acid rain.
Derived from burning of gasoline, natural gas, coal, oil, etc. Cars are an important source, as are gas stoves and water heaters. Los Angeles is the only metro area that exceeds EPA limits. A weak oxidizing agent and by itself has no demonstrable effect on exercise. However, high levels can increase airway resistance, respiratory problems, including lung damage.
Carbon Monoxide (CO)
This odorless, colorless gas is produced in large amounts by industries and motor vehicles.

Burning of gasoline, wood, natural gas, coal, oil, etc. Cigarettes are an important source, with sidestream smoke containing more CO than directly inhaled smoke. CO emissions have decreased 30% in past decade.

Decreases oxygenation. Impairs athletic performance by impeding O2 delivery, CO binding to hemoglobin to form carboxyhemoglobin. May be particularly hazardous to people who have heart or circulatory problems and those with respiratory disorders.
Particulate Matter (PM-10)
This term refers to dust, smoke, soot, and other particles less than 10 microns in diameter.

Fossil fuels, dirt, burning wood, industrial plants, and agriculture (ie, plowing, burning off fields).

These tiny particles can get past the nose and pharynx and settle deep in the lungs. They cause nose and throat irritation, lung damage, and bronchitis. Extracts of industrial PM-10 have been shown to be mutagenic in human cells.
Sulfur Dioxide (S02)
Heavy, colorless, water-soluble gas forms sulfuric acid and acid rain.

Burning of coal, oil, and gasoline, and from industrial residues, especially paper and pulp. 

Decreases mucocilliary function and increases bronchoconstriction. Causes breathing problems and can result in permanent damage to lungs.
Soft, gray-white, slightly water-soluble metal is common throughout nature but can cause devastating health problems, especially in children.
Found in leaded gasoline, old paint, smelters (ie, metal refineries), and lead storage batteries. Also common in soil and old lead pipes. Poisons essential enzymes, causes protein denaturation, and leads to cell death and tissue inflammation. Children are at greatest risk because changes occur at lower blood lead levels.
Volatile Organic Compounds (VOCS)
Smog-forming chemicals that include benzene, toluene, methylene chloride, and methyl chloroform.

Released from gasoline, oil, wood, coal, natural gas, solvents, paints, glues, and many consumer products like hairspray, charcoal fluid starter, plastic popcorn packaging and other products.

In addition to ozone (smog) effects, many VOCs can cause serious health problems.

BAD AIR DAYS / Nina J. Karlin, William W. Dexter, MD / Your Patient and Fitness. Vol 10. No 4. July / August 1996