Health effects of outdoor air pollution.

One hundred sixty-four million Americans live in areas that fail to meet the National Ambient Air Quality Standards for six common air pollutants: particulates, sulfur dioxide, carbon monoxide, nitrogen dioxide, ozone and lead. The impact of these pollutants on health is significant. A Pollutant Standards Index (PSI) ranging from 0 to 500 is used to monitor air quality. When the PSI exceeds 100, the acceptable federal standard has been exceeded by at least one of four measured pollutants. When this occurs, all individuals should be advised to curtail physical activity between late morning and sunset and to remain indoors if possible. Athletes should be encouraged to train in the early morning, when photochemicals are usually at their lowest levels.