Overview of the Children's Health Study

This page updated September 13, 2004

  Why did the Air Resources Board Sponsor the Children's Health Study?

The Air Resources Board (ARB) sets California's ambient air quality standards (AAQS) to protect the most sensitive subpopulations; such as children, the elderly, or people with a pre-existing disease, for example cardiac patients or asthmatics. However, there was a concern that these standards do not adequately protect Californians from the impacts of long-term exposure to air pollutants.

Historically, the focus of air pollution health effects research has been to study effects associated with short-term exposure (often as short as hours) to relatively high concentrations of ambient air pollutants. When viewed from this perspective, air pollution control strategies have proven to been relatively effective. In many areas of California the frequency of exceedance of the AAQSs and the peak concentrations recorded have decreased markedly. As a result, the acute respiratory effects and other short-term consequences of exposure to high concentrations of some air pollutants also appear to be on the decline. However, little information existed on the health effects that may be associated with long-term exposure (measured in years) to low-to-moderate levels of the various pollutants, or combinations of pollutants. It was also not known how repeated exposures to high concentrations of pollutants, especially in combination with other pollutant exposures, affects health.
  How the Children's Health Study fits into the ARB's Research Program

In response to these serious concerns, the ARB began planning the implementation of a major study to determine the impacts of long-term air pollution exposures on children's respiratory health. Children were selected for study because they are especially vulnerable to air pollution; their respiratory and immune systems are still developing and they tend to have higher exposures to pollutants because they breathe faster than adults and generally spend more active time outdoors. The Children's Health Study (CHS) [The official title of the study is "Epidemiologic Investigation to Identify Chronic Health Effects of Ambient Air Pollutants in Southern California."] was initiated in 1991 as a ten-year study.It was subsequently extended until 2004 with ARB funding and has since been additionally extended with funding from the National Institute of Environmental Health Sciences. The ARB will continue to work in collaboration with the investigators through assistance with the monitoring network. Dr. John Peters, at the University of Southern California, directs the study with the collaboration of many investigators at a number of organizations.
  The Children's Health Study - An Overview

The CHS was designed to determine whether children growing up in southern California and exposed, long-term, to the area's unique mixtures and concentrations of ambient air pollutants showed evidence of measurable effects on lung function or identifiable adverse health effects, especially chronic respiratory conditions. The CHS was designed to study the effects of ozone (O3), nitrogen dioxide (NO2), and particulate matter (PM) less than 10 micrometers in aerodynamic diameter (PM10), as well as vapor phase strong acids (i.e., nitric and hydrochloric) and organic acids (i.e., formic and acetic). Later in the study carbon monoxide (CO), the other principle oxides of nitrogen (NO and total NOx), and ultrafine particulate matter (counts of particles smaller than one micrometer in diameter) were added to the pollutants of interest. These pollutants were selected because they appeared to have a higher potential for respiratory health effects.

The study was designed as a three phase process. In Phase I the investigators determined the project parameters, including the final list of pollutants to study, and the specific populations and communities to be included. The second phase, a two-year cross-sectional study, focused on providing an initial understanding of possible changes in health status that might occur over time as a result of air pollution exposure. It also sought to provide the information ARB needed to determine whether health-based AAQSs are necessary for acidic atmospheric pollutants. The third phase was the ongoing observation of changes in health status in relation to air pollutant exposure. During this, the longest part of the study, the investigators were seeking to acquire more precise data regarding conditions of exposure (including the children's activity levels) that lead to specific health effects. The contribution of various pollutants to specific health conditions was also considered. The major reports for this study are available at these links:
Phase II report, Phase III report.

Study Region

Twelve communities in southern California were selected from 86 possible locations, based primarily on their pollution exposure profile and demographic characteristics (e.g., population stability, proportion of the population that were school-aged children). Three relatively non-polluted communities were also included as controls to provide statistical balance with the nine other more polluted communities.

Figure 1

Figure 1 shows the study region, which includes Atascadero (ATA), Lompoc (LOM), Santa Maria (STM), Lancaster (LAN), Long Beach (LON), San Dimas (SAN), Upland (UPL), Mira Loma (MIR), Riverside (UCR), Lake Arrowhead (LAR), Lake Elsinore (LEL), and Alpine (ALP).


Study Population, Health and Exposure Assessments

The study initially began with 3600 school-age children, recruited from the fourth, seventh, and tenth grades. An additional 2000 fourth grade children were added in 1995, to compensate for the children graduating from high school and the anticipated 10 percent annual attrition rate. The children were followed for up to eight years or until they graduate from or leave high school. To recruit the children, the researchers identified schools and teachers interested in participating in the study and made presentations to both students and teachers on lung health and what the study would involve. After the lecture, all the children in the classroom were invited to participate in the study. The parents of those interested students were provided with a questionnaire and parental/legal guardian consent form, which, when completed, enrolled the children in the study. Figure 2 shows one of the researchers explaining how the lungs work, with the teacher and children looking on.

Figure 2
researcher explaing and teacher and children watching


Health Assessments

The health status of the children was assessed through a series of questionnaires, pulmonary function testing, and monitoring of school absences to determine the frequency and severity of respiratory-related illnesses.

An annual questionnaire was used to acquire medical information on the child and other family members, including such things as whether the child suffered from hay fever, wheeze, chronic cough, had ever been diagnosed as having asthma, and/or had any asthma-related problems in the previous year. There were also questions that assessed basic demographic information, such as the number of siblings or changes in residence or the number of people in the household.

A pulmonary function test determined the size and health of their lungs. This was very simple and could be done in the classroom, using a device called a spirometer. The children, especially when they were younger, were always very interested in the results of theirs and their classmates lung function tests. The photo in Figure 3 shows children gathering around a classmate about to perform her test. Figure 4 shows children performing their pulmonary function tests in the school library.

Figure 3
children gathering around classmate about to perform test

Figure 4
chldren performing their pulmonary function tests

  The project included monitoring of school absenteeism to assess occurrences of acute respiratory illnesses, such as asthma or respiratory infections. Schools reported absences among the children, then a portion of those absences are followed-up with telephone calls to the parents to find out whether the absence was due to a respiratory illness or other health-related problem. This element of the project proved to be very labor intensive; therefore, the U.S. Environmental Protection Agency, Health Effects Research Laboratory shared funding for this portion of the work.
  Exposure Assessment

The accurate assessment of the children's exposures to air pollution was as critical to the success of the study as the accurate measurement of the children's health. Estimates of the children's exposures were based on direct measurement and indirect modeling of the pollutant levels in areas (both indoor and outdoor) where the children spent time (e.g., classrooms, playgrounds, neighborhoods, and homes). The children's usual physical activity levels within these environments were also considered a factor.

To assess community pollutant levels, a central monitoring location in each of the 12 communities was outfitted with all the necessary instruments to provide the data required by this study. Among the 12 central sites, seven were part of the existing statewide routine monitoring network and required only augmentation with additional instruments specificly needed for the study. Five of the 12 CHS sites were entirely new because the existing community monitoring sites were not believed to adequately represent concentrations of pollutants where the children live and attend school. This network of monitoring locations was managed by ARB Research Division staff and operated by local air quality districts and contractors. Over the years, the ARB Monitoring and Laboratory Division also contributed significantly to the upkeep and operation of this network.

Hourly data for most pollutants was collected. Vapor phase strong acids (i.e., nitric and hydrochloric), PM2.5, and organic acids (i.e., formic and acetic) were collected as two-week integrated measurements. In addition to information on the pollutants, data were collected on site or compiled from various databases for temperature, relative humidity, wind speed, and wind direction.

To assess concentrations at and in the specific schools the children attended in 1995, the indoor and outdoor concentrations of ozone were measured in two or more classrooms at 54 schools across the 12 communities. An additional separate but integrated study to assess air pollution concentrations in a sample (150) of the children's residences was sponsored by the ARB in 1995. In that study, PM10 and/or PM2.5 were evaluated inside and outside the homes, and air exchange rates were measured within each home. Indoor formaldehyde levels were also measured at some homes.

Other exposures, such as environmental tobacco smoke, and factors that influence potential exposure, such as housing characteristics and activity patterns were assessed by questionnaires administered annually to each of the approximately 5000 children participating in the study. Some direct measurements of children's personal exposures to ozone were also made using small devices carried by the children in backpacks.

The study also investigated how the proximity of roadways to schools and residences, as well as the traffic density on those roadways, impacts the children's potential exposure to vehicular emissions and what effect these exposures may have on the children's health.

Results and Conclusions fro the Study

Findings of the CHS support the following:

  • Air pollution harms children's lungs for life. Children exposed to higher levels of particulate matter, nitrogen dioxide, acid vapor and elemental carbon, had significantly lower lung function at age 18, an age when the lungs are nearly mature and lung function deficits are unlikely to be reversed.
  • Children that were exposed to current levels of air pollution had significantly reduced lung growth and development when exposed to higher levels of acid vapor, ozone, nitrogen dioxide and particulate matter which is made up of very small particles that can be breathed deeply into the lungs.
  • Children living in high ozone communities who actively participated in several sports were more likely to develop asthma than children in these communities not participating in sports.
  • Children living in communities with higher concentrations of nitrogen dioxide, particulate matter, and acid vapor had lungs that both developed and grew more slowly and were less able to move air through them. This decreased lung development may have permanent adverse effects in adulthood.
  • Children who moved away from study communities had increased lung development if the new communities had lower particulate matter levels, and had decreased lung development if the new communities had higher particulate matter levels.
  • Days with higher ozone levels resulted in significantly higher school absences due to respiratory illness.
  • Children with asthma who were exposed to higher concentrations of particulate matter were much more likely to develop bronchitis.
  The results of this study are expected to help guide public health policy that will better ensure protection of children and all Californian's from the effects of long-term exposures to air pollution.

 For further information, please contact: Clint Taylor at (916) 323-1527.

Research Activities

The Children's Health Study