It's worse than dirty Dirty air has toxic components - L.A.'s notorious air pollution is hardest on kids. The closer to a freeway they live, play or attend school, the more likely it is that their developing lungs' capacity will be reduced.

But what many may forget is that the dismal reports of L.A.'s air pollution only capture the average amounts of toxins in the air, and that some places within the urban sprawl are far dirtier than others. Official numbers do not take into account the fact that pollutants are at much higher levels within a few hundred feet of the freeways that crisscross the city -- and for the adults and kids who live, work or go to school there, the effects add up.

For kids, whose lungs are still growing, these effects can be especially damaging.

Mounting scientific evidence reveals that exposure to air pollution interferes with the development of children's lungs, reducing their capacity to breathe the air they need. Although the long-term consequences aren't known, it is known that growth in lung function is nearly complete by the end of adolescence.

Because lung capacity diminishes as people grow older, children exposed to air pollution may enter adulthood with the deck stacked against them.

Proximity to freeways appears to matter. Recently, studies have shown that the lung capacity of children who live within 500 meters (1,650 feet) of a freeway is significantly reduced compared with those who live more than 1,500 meters (4,950 feet) away.

For kids who already live in an area with high levels of pollution, living near a freeway is "adding insult to injury," says Dr. John Balmes, professor of medicine at UC San Francisco and professor of public health at UC Berkeley.

To help protect children from the heightened effects of this extra dose of air pollution, California passed a law in 2003 prohibiting schools from being built within 500 feet of major roadways. Districts are allowed to build within this buffer zone only if space limitations leave no option or the district can find ways to mitigate the increased air pollution. Yet a September article in The Times reported that the L.A. Unified School District was building five schools within 500 feet of a freeway and had plans for two more.

The district is now reconsidering its plans and working on new policies aimed at limiting students' exposure to pollution at schools built near freeways, but such laws can do only so much. Even if they aren't going to school near a freeway, children may still be walking down the street or playing in their backyard near one. Thousands will still be exposed to dangerous levels of air pollution.