The findings were published on the American Thoracic Society's Web site ahead of the print edition of the American Journal of Respiratory and Critical Care Medicine.

Asthma exacerbations are known to be triggered by air pollutants, but researchers are still trying to disentangle which specific pollutants are to blame, and the extent to which they increase pediatric emergency department visits for asthma.

"Characterizing the associations between ambient air pollutants and pediatric asthma exacerbations, particularly with respect to the chemical composition of particulate matter, can help us better understand the impact of these different components and can help to inform public health policy decisions," said lead author Matthew J. Strickland, Ph.D., M.P.H., assistant professor of environmental health.

The researchers obtained data on metropolitan Atlanta emergency department visits for asthma exacerbations in children between five and 17 years of age between 1993 and 2004 and used data on ambient pollutant collected as part of the Study of Particles and Health in Atlanta (SOPHIA). They then analyzed the more than 90,000 asthma-related pediatric emergency department visits with respect to the ambient levels of 11 different pollutants. The availability of daily monitoring data on particulate matter components allowed them to develop a detailed picture of pollutant concentrations and subsequent effects on emergency department visits for pediatric asthma exacerbations.

Ozone was strongly associated with an increase in pediatric asthma exacerbations during the summer, and there was evidence of a dose-response relationship beginning with concentrations as low as 30 parts per billion.

Importantly, the current EPA 8-hour ozone standard is based on the three-year average of the fourth-highest measured concentration at any monitor, which must not exceed 75 ppb. Ozone concentrations in many urban areas throughout the U.S., including metropolitan Atlanta, routinely exceed the EPA standard.

Several markers of pollution from combustion engines -- i.e., pollutants emitted from the tailpipes of cars and trucks -- were also associated with pediatric emergency department visits for asthma exacerbations during the warm season. When they analyzed the effects of multiple pollutants together, the researchers found evidence that ozone and primary pollutants from traffic sources independently affected pediatric asthma exacerbations.

The researchers offered several possible explanations for why the pollution effects appeared stronger in the warm season, noting that "during the summer children are more likely to play outside" and postulating that there may be an "unidentified synergism between the pollutant and a meteorological or physical factor." Overall rates of emergency department visits for pediatric asthma increased by 60 percent in the cold season, probably because of the important role that respiratory infections have in triggering exacerbations.

"In this study we observed evidence that ambient concentrations of ozone and primary pollutants from traffic sources independently contributed to the burden of emergency department visits for pediatric asthma," wrote Dr. Strickland. "Further, the associations were present at relatively low ambient concentrations, reinforcing the need for continued evaluation of the EPA's National Ambient Air Quality Standards to ensure that the standards are sufficient to protect susceptible individuals."

Note: If no author is given, the source is cited instead.

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