The 10-year-long Children's Health Study is considered one of the nation's most comprehensive studies to date of the long-term effects of smog on children.

The new findings address the development of lung function in children, showing that, in polluted areas, their lung function growth lags behind that of children in areas with cleaner air. Lung function is a medical term describing lung capacity and how well lungs are working.

"These findings are an important confirmation of our earlier studies," said W. James Gauderman, an associate professor of preventive medicine at USC and the study’s lead author. "The results further strengthen the evidence that breathing polluted air has a negative effect on the developing lungs of children."

Preventive medicine researchers from the Keck School of Medicine of USC have monitored levels of major pollutants in a dozen Southern California communities since 1993, while carefully following the respiratory health of more than 3,000 students. The latest report, released in the July 1 issue of the American Journal of Respiratory and Critical Care Medicine, covers smog's health effects on a group of children from 1996 to 2000.

Each year, USC scientists have tested lung function by having each child take a deep breath, then measuring how much and how fast kids blew out the air. Children’s lung function usually grows steadily until they reach adulthood.

Children with decreased lung function may be more susceptible to respiratory disease and may be more likely to have weaker or smaller lungs and have chronic respiratory problems as adults.

"Given the public health importance of these findings, it’s imperative that we accelerate our efforts to achieve clean air in Southern California," said John Peters, USC’s Hastings professor of preventive medicine and one of the study’s authors.

Researchers have found that, on average, lung function growth tends to be higher in cleaner communities and lower in areas with more air pollution.

The latest study followed 1,678 children who were in fourth grade in 1996. Researchers found that over the following four years – as children went from age 10 to 14 – the lung function growth rate of children in the most polluted community was about 11 percent lower than that of children in the least polluted community.

This is similar to the 10 percent lower growth rate that Children’s Health Study investigators previously reported based on a group of 1,498 fourth graders followed from 1993 to 1997.

Similar effects on lung function were observed in boys and girls, and in asthmatic and healthy children.

"As in the previous study, we found that the association of slower lung function growth with air pollution also was stronger in children who spent more time outdoors," said Gauderman. "This is what we would expect if outdoor air pollution is having a detrimental effect on children’s lungs."

Acid vapor was a key offender in both the current and previous studies, Gauderman notes. Acid vapors encompass nitric, formic and acetic acids and, like other pollutants, come directly or indirectly from vehicles burning fossil fuels, emissions from industrial plants and other sources.

Nitrogen dioxide, fine airborne particles known as PM2.5 and elemental carbon also were strongly associated with reduced lung function growth. Much of the elemental carbon in the Southern California air comes from combustion of diesel fuel, so the link to carbon might hint at a general association between lung function and exposure to diesel exhaust particles such as those from trucks.

The latest findings also showed a link to ozone levels.

Millions of Southern Californians breathe polluted air every day, especially on days when levels of pollutants exceed state and federal standards for air quality. The area's layout as a basin, as well as the typical sunny weather and omnipresent vehicle traffic, combine to keep high levels of pollutants in the air. Although polluted air has long been known to cause immediate symptoms such as eye irritation, coughing and chest tightness, long-term or chronic effects have been less clear.

Future research might find relationships between short- and long-term effects.

"Children in a community with high levels of pollution will be more likely than those in areas of cleaner air to be exposed to sudden episodes of very high concentrations of pollutants," said Gauderman. Often, children have acute respiratory symptoms on high-smog days, and researchers plan to investigate whether reduced lung function growth rates might be a consequence of many acute respiratory reactions over time.

The researchers will continue monitoring students as they mature to see if pollution-related deficits in lung function growth persist into adulthood, resulting in a lower level of maximum adult lung function and, perhaps, increased risk of respiratory illness.

For this study, the California Air Resources Board routinely tests air in 12 communities, from Atascadero in the north to Alpine in the south. Locations in the Inland Empire were chosen because they were known to have relatively high levels of pollutants, while northern communities were chosen because they have lower pollution levels.

Over the last two decades, air quality in Southern California has improved. "These latest findings emphasize the need to continue the clean-up efforts," said Gauderman.

The study was undertaken with support from the California Air Resources Board. The National Institute of Environmental Health Sciences, the Environmental Protection Agency and the Hastings Foundation provided additional funding.

For more information about the Children's Health Study, visit the researchers' Website at: www.usc.edu/medicine/scehsc.

W. James Gauderman, Frank Gilliland, Hita Vora, Edward Avol, Daniel Stram, Rob McConnell, Duncan Thomas, Fred Lurmann, Helene G. Margolis, Edward B. Rappaport, Kiros Berhane and John M. Peters, "Association between Air Pollution and Lung Function Growth in Southern California Children: Results from a Second Cohort," American Journal of Respiratory and Critical Care Medicine. Vol. 165, No. 13, July 1, 2002.