Everyone is familiar with the gray-brown haze that often blankets Los Angeles, and the fact that the city consistently ranks as one of the most polluted in America.
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.
Stunted lung development
In 2004, USC researchers reported that children living in areas with higher pollution, such as San Dimas and Riverside, had stunted lung development compared with children living in areas with lower pollution, such as Atascadero and Alpine.
The findings came from the Children's Health Study, which in 1993 recruited about 1,700 fourth-graders from 12 California communities and studied their lung function over eight years.
The effects on children's lungs were both statistically and clinically significant: The proportion of children with low lung function was 4.9 times greater in the community with the highest level of fine-particle pollution (Mira Loma) compared with the community (Lompoc) with the lowest levels (7.9% versus 1.6%). Results were similar when the researchers looked at other categories of pollution, such as nitrogen dioxide and elemental carbon.
In February, the USC group published another report, in the journal the Lancet, showing that living near a freeway could further affect a child's lung development.
As in the 2004 study, researchers followed the group of fourth-graders recruited in 1993, as well as a later group recruited in 1996. In this study, however, the children in each city were further subdivided into those who lived close to (within 500 meters) or far (more than 1,500 meters) from a freeway or other major road.
As in the other study, researchers would visit the children every year at their schools and measure with a device called a spirometer how much and how fast each child could exhale.
They found that children who lived close to a freeway in a low-pollution community had about a 4% decrease in their lung function compared with children living in the same community but far from a freeway. This decrease was similar to that seen in children who lived in highly polluted communities but far from a major road.
The results were worst for the children who lived near a freeway within a polluted city. They had the greatest reduction in lung function over the course of the eight years each child was tracked -- about 9%, compared with the kids in clean cities who lived at least 1,500 meters from a major road.
Lung development is nearly complete by age 18 -- meaning that someone with a deficit in lung function at the end of adolescence will probably continue to have less than healthy lung function for the rest of his or her life. And that could lay the adult open to a variety of maladies.
"Poor lung function in later adult life is known to be a major risk factor for respiratory and cardiovascular diseases, as well as for mortality," said W. James Gauderman, an epidemiologist at the USC Keck School of Medicine and leader of both studies.
The results of the USC study make sense, given what scientists know about the concentrations of tailpipe pollutants near major roads.
Jean Opital, an officer for the South Coast Air Quality Management District who evaluates studies on the health effects of air pollution, says that pollution concentrations are highest in the first 150 meters of a large road but then start to drop off. But calculations predict that to get down to the levels seen upwind of a freeway, you have to get about 1,000 meters (3,300 feet) away.
"Though we in L.A. don't have the best air quality, proximity to sources does matter, " he says.
Taking in more pollutants
Children are especially vulnerable to air pollution because they breathe more rapidly than adults relative to their body weight and lung size. This results in exposure to a relatively larger dose of any air pollutants. Kids also spend a lot of time engaged in vigorous physical activity, leading to even heavier breathing.
When they play hard, they tend to breathe more through their mouths, bypassing the natural filtering effects of the nose, allowing more pollutants into their lungs. And unlike adults, who are likely to stop their activities when effects of pollution such as wheezing and coughing set in, children often keep going -- continuing to expose themselves to pollution.
The heady brew they are exposed to has various toxic components -- carbon monoxide, sulfur dioxide, nitrogen dioxide -- and the two that pose the greatest threat to human health: ground-level ozone and particulate matter.
Ground-level ozone is formed by a chemical reaction between volatile organic compounds and oxides of nitrogen emitted by cars and other sources such as power plants that takes place in the presence of sunlight. In L.A., the onshore breeze usually pushes the ingredients of ozone farther inland. But calm days provide the perfect conditions for a blanket of ozone to cover the city.
Exposure to ozone can cause immediate effects such as coughing, throat irritation and difficulty breathing.
It can also worsen asthma attacks and increase the susceptibility of the lungs to infections, allergens and other air pollutants -- making exposure especially risky for those with asthma and other lung conditions such as chronic obstructive pulmonary disease.
Particulate matter in the air is a mixture of solids and liquid droplets that vary in size. Particles larger than 10 microns (about one-tenth the diameter of a human hair) do not usually reach a person's lungs, but they can irritate the eyes, nose and throat.
Exposure to "coarse" particles (in the range of 2.5 to 10 microns in diameter) and "fine" particles (less than 2.5 microns in diameter) can aggravate heart and lung diseases.
A study of more than 4,000 Swiss adults ages 18 to 60 during the course of 11 years, which appeared last week in the online edition of the New England Journal of Medicine, has shown that the inevitable decline in lung function seen in adults is lessened in those who are exposed to reduced levels of particle pollution.
The smallest particles of all -- so-called "ultra-fine" particles -- are of increasing concern to air pollution experts. Air levels of these tiny bits of air pollution, which measure less than 0.1 micron or one-thousandth the diameter of a human hair, are not regulated by state or federal agencies, and their health effects are only now beginning to be understood.
What researchers do know is that ultra-fine particles travel far deeper into the lungs than other types of particle pollution. They can even pass through the lining of the lungs, gaining access to the bloodstream. This allows them to travel to other organs and possibly interfere with their function.
Ultra-fine particles might also make their way into the brain, USC's Gauderman says. He says there is some suspicion in the research community that they can actually travel straight to the brain through the olfactory nerve at the top of the nasal passage.
They are so small that standard air filters cannot remove them. "They act like a gas, getting in around doors and windows," Gauderman says.
When pollutants are inhaled, gases such as ozone and the chemicals stuck to the surfaces of various sizes of particulate matter react with molecules in the lungs, injuring cells. The body's response to this injury is inflammation, which causes the airways in the lungs to constrict.
Children have narrower airways than adults, so pollution that might cause only a mild inflammatory response in an adult can significantly constrict the airways in a young child. This can be especially dangerous for children with asthma.
Long-term exposure to air pollution can cause chronic inflammation. In response, the body will attempt to wall off the damaged parts of the lungs, creating tissue that's less pliable than healthy tissue. That, Balmes says, explains why decreased lung function like that seen in the Children's Health Study comes about.
"It's basically a scarring process," he says.
Reducing risks at schools
Angelo Bellomo, head of the Office of Environmental Health and Safety for the Los Angeles Unified School District, says his office is taking the dangers posed by freeway pollution seriously.
"We've got to do everything we can do that is within our power to reduce that risk," he says.
As a start, his office has begun taking ultra-fine particles, which were not previously considered, into account when analyzing new locations for schools.
There are more than 70 district campuses within 500 feet of freeways, housing more than 60,000 students. Bellomo's office is compiling a list that ranks the schools by level of risk based on the number of students, the number of years students spend at the school, distance to freeways and the volume of diesel trucks that travel the nearby freeways.
The office will be developing a range of options and associated costs for upgrades to existing schools that would reduce school occupants' exposure to nearby sources of air pollution. Its report is due at the beginning of March.
Bellomo says his office will be looking at all options, including some promising new filtration technologies.
He admits that the school district can't do much to reduce the risks of air pollution when children are outside, but he aims to reduce the risks indoors enough so as to offset the outdoor exposure.
The district will do what it can, Bellomo says, but the most effective way to reduce the risk from freeway pollution for children would be for state and federal regulators to enact rules that reduce pollution at the source.
Angela Beach, 41, of Sherman Oaks, will be following the district's progress.
Her 6-year-old son, who suffers from chronic asthma, attends Hesby Oaks School, a recently reopened campus in Encino that is within 500 feet of the 101 Freeway. Firmament Avenue, a bit of greenbelt and a sound wall are all that stand between the athletic fields and the constant rush of cars on the 101 and 405 interchange.
Beach says her son's asthma was well controlled when he was in preschool. He didn't have trouble playing outside like all the other children.
But now, she says, "he just can't do it."
The effects of the pollution near the freeway aren't just physical for her son, Beach says. He doesn't understand why he can't play at school. He gets frustrated and angry when he has to abandon basketball practice because he can't get the air he needs. Beach has had to explain to his coach that it isn't that he doesn't want to play, it's that he's isn't able to.
Beach says her daughter, who is 8 and does not have asthma, has also commented on the changes on her body since she started at her new school, even though the issue of air quality is never discussed with her. She comes home from school, Beach says, and tells her mother how she struggles on the playground, complaining, "It's harder here," comparing Hesby to her previous school, Sherman Oaks Elementary, which is just shy of a mile from the 101 and 405 freeways.
Beach wants the district to do all it can with filtration systems at Hesby and other schools. She is also lobbying the city and school district to plant trees behind Hesby because some research has shown that they could absorb some of the pollution that is flowing into the outdoor hallways and lunchroom of the campus.
"These," Beach says, "are problems that affect the lives of every child, forever."
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Trees may help fight pollution
Can trees help fight smog? Thomas Cahill, a professor of physics and atmospheric sciences at UC Davis, has results suggesting they can reduce levels of ultra-fine particle pollution near freeways.
He has found that in windy conditions, trees along the side of a freeway can help mix the air and dilute the concentration of ultra-fine particles. In calm conditions, trees seem able to capture the particles, preventing them from traveling to nearby homes or schools.
Cahill says that once ultra-fine particles stick to the leaves of trees, they will not blow off. Instead, they will remain on the tree until the leaves drop or they are washed away in the rain.
He says that other researchers have not been interested in looking at trees as mitigation for ultra-fine particles because older research had shown that trees could not block fine particles (which are about 25 times larger than ultra-fine particles) from blowing off roadways.
Cahill says it's important to use the right trees to block ultra-fine particles. Some trees may not absorb enough particles. Others emit chemicals that can contribute to ozone formation. Trees with lots of needles, such as redwoods and deodar cedars, he says, are best.
-- Erin Cline Davis