FRIDAY, April 25 (HealthDay News) -- Even when air pollution levels are within current air quality standards, inner-city children with asthma suffer, a new study finds.

The Inner City Asthma Study Group researchers, who looked at 861 children, ages 5 to 12, with persistent asthma, said their findings raise questions about current air quality standards in the United States. They suggest that asthma management plans for inner-city children may need to include reduced exposure to air pollutants.

For two years, the researchers monitored the asthma symptoms of children living in low-income inner-city sections of Boston, New York CIty, Chicago, Dallas, Seattle and Tucson.

These youngsters had significantly decreased lung function following exposure to higher concentrations of air pollutants such as sulfur dioxide, airborne fine particles, and nitrogen dioxide. The study also found that higher nitrogen dioxide levels and higher levels of fine particles were associated with asthma-related school absences, and that higher nitrogen dioxide levels were associated with an increase in asthma symptoms.

Since motor vehicle exhaust is the main source of nitrogen dioxide, the findings suggest that car emissions may be causing respiratory problems among inner-city children with asthma, the researchers said.

The study, supported by the U.S. National Institutes of Health and Environmental Protection Agency, was published in The Journal of Allergy and Clinical Immunology.