Hundreds of studies link air quality to asthma and other respiratory problems. High levels of ozone irritate lung passages, causing coughing, wheezing, chest tightness and shortness of breath. This smog triggers asthma attacks, respiratory diseases, and is linked to premature deaths in children and adults.

Children are of special concern because they inhale more air than adults, and because they extract more ozone from the air they breathe. [CARB 2005] Preliminary studies in smoggier communities of Southern California have found that ozone may cause asthma in previously healthy, athletic children. [McConnell 2002] Children who grow up in smoggy regions have permanently scarred lungs, and feel lifelong effects of diminished lung capacity. [Kunzli 1997]

In the U.S., vehicles are the main source of pollutants that cause the smog that triggers asthma and respiratory problems. Previous attempts to control pollution from automobiles have had measurable benefits to air quality and health. Scientists calculate that efforts to reduce smog pollution in Southern California have already prevented more than 3 million school absences a year, and provided an economic benefit of more than $245 million. [Hall 2003] Indeed, today's cars are hundreds of times cleaner than cars produced 30 years ago. However, both the number of miles driven and the number of cars owned by Americans have risen steadily, slowing any progress toward a net reduction in pollution. Further improvements to car performance are necessary to continue the trend toward cleaner air.

Air quality scientists calculate that vehicles are the major contributing source of precursor chemicals—volatile organic compounds (VOCs) and nitrogen oxides (NOx)—that react in the atmosphere to form smog. Long-term studies, many from "ground zero" in California, link everyday pollution from vehicles with the development and severity of asthma in children.

The Southern California Children's Health Study found that children living a quarter mile from a freeway had an 89 percent greater chance of being diagnosed with asthma compared to children living a mile away. [Gaudeman 2005] This risk was attributed to nitrogen dioxide emissions from vehicles. Nitrogen dioxide is one of the nitrogen oxide precursor chemicals that reacts to form ozone.

Another look at the same group of children found that children living within 250 feet of major roads had a 50 percent higher risk of having had asthma symptoms in the past year compared to those living 2 to 3 times further from similar sized roads. [McConnell 2006]

In the San Diego area, researchers found that asthmatic children residing in high traffic areas had more frequent asthma-related doctor visits than children in lower-traffic areas. The same group reported a two-fold increase in asthma rates for children living on streets with the highest traffic density relative to children on less traveled streets in the same area. [English 1999]

In the San Francisco Bay Area, researchers found a statistically significant relationship between traffic-related pollution and respiratory symptoms in children, despite relatively low pollution levels for all children and very small differences in pollution exposure between the participants. [Kim 2004]

Many of California's schools are located near freeways and other high traffic streets. Idling school buses and long lines of parents dropping off their children make schools a hot spot for vehicle pollution. One study found that 1 in 8 California students (721,363 children) attends a school with more than 25,000 vehicle trips per day on adjacent roads. [Green 2003] A smaller group, 150,000 students, attends schools near streets with more than 50,000 vehicle trips each year. [Green 2003]

Vehicles are the source of many pollutants, but smog-forming emissions from vehicles are of particular concern.

A six-month study of fourth graders in 12 Southern California communities found an 83 percent increase in respiratory-related absences when daytime ozone levels increase by 20 parts per billion. [Gilliland 2001]. Changes in other common air pollutants were not associated with an increase in school absences. Nationally, asthma is the leading cause of missed school days, accounting for one-third of all absences. [EPA 1991] In Los Angeles County alone, smog is blamed for more than 1 million school absences a year. [CARB 2005]

The current ozone concentrations in some regions of Southern California appear to be sufficient to trigger asthma in previously healthy individuals. Following 3,535 healthy, athletic children, researchers found that those who participated in 3 or more sports per year had a 3.3-fold increase in the likelihood of being diagnosed with asthma when compared to less active children in the same community. [McConnell 2002] The effect was more dramatic for children playing high-activity outdoor sports rather than lower-activity sports, and less dramatic in a second group of communities with cleaner air. [Peters 2004]

Even when they don't cause asthma, children's exposure to smog has life-long effects on lung development. Animal studies indicate that ozone exposure during lung development causes long-term inflammation, disrupts growth factors, and creates fibrosis and alters lung architecture. [CARB 2005 citing Barr 1990, Schelegle 2003] These findings have recently been confirmed in studies of young adults. Researchers examined lung capacity of first-year students at U.C. Berkeley and Yale University. They reported noticeable reduction in the lung capacity of students who grew up in polluted regions compared to those who were raised in areas with cleaner air. [Kunzli 1997, Tager 1998, Galizia 1999] The Yale students who spent at least 4 years in regions with high summertime ozone levels had significantly worse lungs than their peers. [Galizia 1999, Kinney 1998]

Since lungs form throughout childhood, they are susceptible to damage during the entire period. By the early 20s lungs are fully formed, and it is unlikely that pollution-related impacts measured in 18 year-olds will be repaired during adulthood. College students with lung damage already reported more respiratory illness as young adults, and these impacts will lead to more serious respiratory disease as they age. Lung function is also a major determinant in life expectancy in the elderly.

All children deserve clean air

When smog levels rise, asthmatics use more medication, have more respiratory illnesses, and visit the doctor, emergency room or hospital more frequently. However, the relationship between air quality and asthma severity is also strongly linked to economic and social inequities. [O'Neill 2003] Numerous studies have found that poor and non-white members of the population reside in areas with the worst air pollution [Morello-Frosch 2001, ALA 2005, Apelberg 2005]

Sixty-one percent of black children, 70 percent of Hispanic children and 68 percent of Asian-American children live in areas that exceed the national ozone standard, while only 51 percent of white children live in such areas. [ALA 2005] These same communities have higher rates of asthma and other respiratory disorders. Many now report that a quarter of all children are diagnosed with asthma in some inner-city neighborhoods and agricultural communities.

Poor families lack access to adequate health care and suffer more severely from asthma and other respiratory problems. When asthmatic children are not able to see a doctor regularly for routine check-ups, and when their parents lack money for expensive medications, there are more trips to the emergency room, and more deaths.

These same children often face more asthma triggers at home, with molds related to leaky plumbing and roofs, pests that create allergenic responses for sensitive lungs, and increased use of irritating pesticides. Poorer students and Latino and African-American children are also more likely to attend schools where the air quality compromised by smog or other air pollution. [Green 2003] Finally, poorer communities are homes to the oldest and most polluting automobiles, and are adjacent to industrial areas with more diesel traffic and idling trucks.

Clearly, the benefits of reducing vehicle pollution will have the biggest impact in communities where racism and economic injustice have led to the most severe problem with asthma.


American Lung Association. 2005. Racial Disparity and Air Quality.

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