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Smoggy Schools
April 20, 2005

Smoggy Schools: Smoggy Schools

Smog has major impacts on both asthmatic and healthy children. Smog causes millions of respiratory illnesses that keep children from attending school each year. It can also trigger respiratory symptoms during exercise and aggravate asthma symptoms. Since children spend most of their day at schools, and often remain in the afternoon to play or participate in a sports league, schools are a major opportunity to establish healthy activity patterns for children, especially those who are at high risk for pollution-related illness.

Asthma has skyrocketed over the past decade, and schools play an increasing role in helping students cope with their condition. Reducing asthma triggers in schools, modifying physical education for asthmatics, and monitoring the use of maintenance medications are increasingly a responsibility of school staff. These activities protect the health of asthmatic students by guaranteeing that they can participate fully in school activities, concentrate on lessons and even attend classes regularly.

Children are much more sensitive to the effects of smog than adults, particularly when they are exercising. Schools need to do more to protect asthmatic and healthy children on especially smoggy days. When ozone levels are severe—more than double the proposed daily safe level—the state advises schools to keep children from playing outdoors. EWG analysis of ozone levels at schools found that 2,800 California schools, serving 1.7 million students, experienced ozone levels this high between 2000 and 2003.

Children not only inhale more air than adults, but they also extract more ozone from the air they breathe. According to the state's review of ozone pollution, ". . . up to eight times the amount of ozone reaches and reacts with target regions of the deep lung in infants compared to adults." [ARB(1) 2005] Ozone levels typically peak during warm days, and in the afternoons, precisely when children spend time playing or exercising outdoors.

The symptoms of exercise-induced asthma may be observable — wheezing, shortness of breath and chest tightness—or they may be more subtle: a cough, congested lungs, or a child who tires easily during exercise. Most asthmatics have difficulty breathing during exercise. However, up to 10 percent of children who have not been diagnosed with asthma also develop breathing problems with vigorous exercise. [Núñez 2005]

Graph: ozone exposure is greater in younger children and peaks during exercise

Playing safely

Given elevated ozone concentrations, particularly in greater Los Angeles and the San Joaquin Valley, school administrators, teachers, school nurses, coaches, day care staff and day camp operators need to take immediate precautions to protect children's health when smog levels peak. Many children will be able to play safely outdoors despite moderate levels of ozone pollution, but it is difficult to identify the children who will be more sensitive to pollution. Adult involvement is needed to limit the duration or intensity of outdoor exercise for some or all children on especially smoggy days.

When ozone levels exceed 150 ppb, schools are advised to limit children's "sustained rigorous exercise" lasting more than an hour. [Vance 2005] Nine counties had ozone levels this high between 2000 and 2003. EWG analyzed air pollution records and addresses for about 12,000 California schools [California Department of Education(1) 2005] and found 1.7 million students attending 2,800 schools where this concentration was exceeded between 2000 and 2003.

Statewide, more than 300,000 students attended schools where smog levels reached the 'exercise warning' level an average of 5 or more times each year. All of the schools were in San Bernardino County. These schools have more non-white students than other schools. There were 20 percent more Hispanic students and 64 percent more African-American students in the 307 public schools with the worst smog levels compared to the other California public schools with a nearby air monitor. [California Department of Education(2) 2005]†1 Two hundred schools that were hit hardest were located in areas where there were 12 warning days in 2003.

Smog levels typically peak on warm days and during the afternoon when children enjoy recess, sports or outdoor play. They may have occurred during a weekend or summer vacation. But summer school, sports leagues and year-round schools guarantee that a fraction of the children will still be at school sites during weekend or summer days. In a handful of cases the average at a California monitor was 150 ppb for the entire day, indicating that pollution concentrations were severe for hours on end.

To estimate smog levels at schools, we matched each school address to the nearest ozone monitor within the same air district, and used the daily or hourly ozone measurements as a proxy for the air quality at each school. Because ozone levels do not vary significantly over a several mile radius, this method gives a reasonable approximation of smog levels at the school site. Three-quarters of schools were within 10 miles of a functioning air monitor. Less than 3 percent of schools (375 schools total) were further than 30 miles from an air quality monitor. Most were excluded from this analysis, except for 85 schools that were included because the nearest ozone monitor was specifically designed to monitor smog concentrations over a regional scale (a 50 to 150 mile radius). [Pan 2005]


Summary of schools where smog exceeded exercise warning levels by county

County Number of Schools with at least one warning day Average number of days between 2000-03 with smog levels greater than 150 ppb Total number of days at the schools with the worst smog
Alameda 48 2 2
Contra Costa 1 2 2
El Dorado 6 1 1
Fresno 80 4.6 5
Imperial 13 2.4 3
Kern 15 3 3
Los Angeles 1229 1.7 3
Madera 13 2 2
Orange 222 1 3
Placer 2 1 1
Riverside 424 6.3 19
San Bernardino 507 14.8 23

It is difficult to gauge the degree to which the air districts' guidance to limit recess and outdoor activity is being implemented by California schools. Southern California school districts are increasingly attuned to daily air quality forecasts, faxed daily by the South Coast Air Quality Management District to local school administrators, providing information to guide scheduling decisions about sports games and recess when levels of smog or other pollutants rise. [Cassmassi 2004] SB25 also required the South Coast Air District to begin informing Los Angeles-area day care centers where practicable.

Efforts to protect children from peak smog levels are hampered in regions where there is inadequate monitoring information to predict daily smog levels. The Latino Issues Forum recently reported that there is no monitoring for the western portion of the San Joaquin Valley, a rural region with predominantly Latino communities. Not a single monitor has been placed between Tracy and Taft, a distance of 230 miles. [Latino Issues Forum 2005]

The price of inactivity

School administrators and coaches must carefully weigh the risks of unhealthy air against another pressing public health issue, the threat that childhood inactivity leads to obesity. They must also consider new evidence of a relationship between obesity and the development of asthma. Researchers in Southern California found that being overweight and obesity were both associated with increased risk of asthma diagnosis. Overweight and clinically obese children had a 52 and 60 percent increased risk of asthma diagnosis, respectively. [Peters 2004] With three-quarters of California's middle-school students unable to meet the minimum physical fitness standards, assessing the risks and benefits of outdoor exercise on smoggy days is a devil's bargain. In the meantime, children are paying a substantial price for smoggy air.

The sheer number of bad ozone days in California communities means that restricting physical activity for young children, while a necessary first step, is no workable long-term solution to protect children's health. Educators and parents must make smart choices about the benefits and risks of children's activity on peak pollution days, but the state must do its part by adopting the proposed long-term ozone standard and making rapid reductions to smog levels a top priority.

Lower-level smog exposures also harm kids

The long-term impacts of less dramatic concentrations of smog pollution also trigger both respiratory illness that causes school absences, and other long-term effects on respiratory health. The proposed standard would require ozone levels to average 70 ppb or lower over an 8-hour period, and would be much more protective of health. Over the four study years California schools have, on average, 23 days where the air quality violates the proposed standard. However, smog levels are not equally distributed over the state. Children in greater Los Angeles and the San Joaquin Valley have much greater daily exposures to ozone than children in other regions. For more than 300,000 children who attend the 416 schools with the worst air quality, their schools have experienced 123 violations of the proposed daily standard each year.

School absences

Another dramatic impact of smog on children's well-being can be measured by school absences attributable to smog pollution. 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 ppb. [Gilliland 2001]. The daytime average ozone level ranged from 31 to 65 ppb in study communities, and occasionally exceeded the proposed standard of 70 ppb over an eight-hour period. This is similar to the average ozone levels in 17 California counties with the worst ozone pollution between 2000 and 2003. Changes in other common air pollutants were not associated with an increase in school absences.

Scientists calculate that past efforts to reduce ozone pollution in Southern California have already prevented more than 3 million school absences, and provided an economic benefit of more than $245 million. [Hall 2003] But further improvements are still possible and necessary. Excessive ozone currently causes 3.3 million school absences each year for California's kids. [ARB(1) 2005] Averting 3 million additional ozone-related school absences each year would have remarkable benefits for California families and schools. Absent children suffer the most, losing chances to learn during the day and play outdoors in the afternoon. The direct economic consequences are measured as the sum of parents' lost wages and lost revenue of school districts who are only paid for students who attend classes.

Projected number of school absences due to excess smog


County Estimated number fewer absences when proposed smog standard is met Estimated annual cost savings
Los Angeles 1,147,760 $114,776,000
Orange 331,500 $33,150,000
San Bernardino 298,740 $29,874,000
Riverside 245,940 $24,594,000
Fresno 158,600 $15,860,000
Kern 153,510 $15,351,000
San Diego 120,000 $12,000,000
San Joaquin 114,400 $11,440,000
Sacramento 87,890 $8,789,000
Stanislaus 92,950 $9,295,000
Tulare 74,750 $7,475,000
Ventura 51,604 $5,160,400
Remaining 46 California counties combined 415,529 $41,552,900

Asthmatic children suffer unduly from air pollution and bear the brunt of smog-related school absences. Asthma is one of the leading causes of school absences for children. Asthmatic children miss on average 4 school days per year because of asthma symptoms. [CAFA 2005] Within the Southern California school study, children who had been previously diagnosed with asthma had two-thirds more respiratory illnesses than non-asthmatic children. [Gilliland 2001] Nationally, asthma is the leading cause of missed school days, accounting for one-third of all absences. [USEPA 1991]

Does exercise in smoggy areas cause asthma in healthy children?

The unique characteristics of ozone pollution, children's lungs and exercise combine to create an exceptional risk for athletic children in smoggy areas. Researchers from the Southern California Children's Health Study surveyed 3,535 children living in Southern California communities. They found that children playing 3 or more outdoor sports in smoggier communities had a 3-fold increase in the risk of being diagnosed with asthma, compared to children in the same communities who did not play outdoor sports. [McConnell 2002] The degree of athletic intensity of the sport was also related to the risk of asthma diagnosis. This research contradicts the long-standing belief that air pollution exacerbated but did not cause asthma. This finding must be replicated in order to confirm this unexpected conclusion. However, it points to the dangerous relationship between smog and exercise for both healthy and asthmatic children.

Traffic and schools

The prevalence of traffic-related pollution at schools leads to another school-specific concern for children's health. Many of California's schools are located near freeways and other high traffic streets. Idling school buses and long lines of parents dropping off or picking up 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, attend schools near streets with more than 50,000 vehicle trips each year. [Green 2003] Nearby roads were determined to be those within 500 feet of the school site. Poorer students, and Latino and African-American children are more likely to attend schools choked with traffic pollution. [Green 2003]

Traffic pollution is strongly associated with ozone and also asthma hospitalizations. During the 17 days of the Atlanta Summer Olympics in 1996, the city took extraordinary measures to limit vehicle traffic, decreasing vehicle trips by 22.5 percent. Scientists found that the daily ozone concentrations dropped from 81 to 59 ppb, a decrease of 28 percent. Asthmatics benefited widely from this improvement. There were 40 percent fewer Medicaid claims filed for asthma and HMO visits. The number of asthma-related emergency room visits dropped by 11 percent and asthma hospital admissions dropped 19 percent. [Frideman 2001] Controlling vehicle and other engine emissions is the most important way of reducing smog in California.


†1 This statistic compares the proportion of American Indian, Filipino, Asian, Pacific Islander, Hispanic and African American students with the proportion of white students. We used enrollment and demographic information available from the California Department of Education. Racial-ethnic data was only available for public schools in California. The comparison group only includes public school students attending a school with a nearby air monitor.