Outdoor Air Pollution

Community air-pollution studies typically evaluate the health effects of routinely measured air pollutants, such as nitrogen oxides (NOx), sulfur dioxides, particles of various sizes (for example, PM10, PM2.5)2 or concentrations (TSP), and in some cases atmospheric transformation products, such as ozone. Some of the studies used single-location measures (or community averages) of air pollutants to characterize exposures of residents of each study community, and a few estimated exposure of individual residents on the basis of interpolation of ambient monitoring data.

Prospective Studies

The Adventist Health Smog study, a prospective cohort study, began in 1976 by following a cohort of 6,000 Seventh-Day Adventists (SDAs) in areas of California with varied air-pollution magnitudes. SDAs are a unique cohort because they are non-smokers (35% of men and 14% of women were smokers before joining the church). The church’s prohibition of smoking reduced the confounding effect of current smoking for studying health effects of air pollution.

The following studies of incidence of respiratory outcomes were based on the SDA cohort. Each study used similar methods and confounding and bias controls. Study subjects were over 25 years old, baptized members of the SDA church, non-Hispanic and white, had lived within 5 miles of their permanent residence for more than 10 years, and resided in San Francisco, the Los Angeles Basin, or San Diego. Participants were studied for respiratory and other health outcomes. Respiratory outcomes were studied in a subcohort of nearly 4,000 people. Three respiratory outcomes were analyzed according to responses to a 21-item symptom questionnaire: asthma, chronic bronchitis, and overall airway obstructive disease (AOD). AOD included asthma, chronic bronchitis, and emphysema (there were so few cases of emphysema that it was not analyzed separately). Each subject’s symptoms were classified as none, possible, and definite3 for each respiratory outcome. Exposure to air pollutants was determined for each participant on the basis of ambient monitoring sites in 1977–1987 by interpolating residential ZIP codes and work-location history. The precision of interpolating concentrations was verified. In 1976, each study participant completed a detailed demographic and lifestyle questionnaire about smoking, occupation, hours spent in driving on highways, and other topics. In 1977 and 1987, each participant completed standardized respiratory-symptoms questionnaires (American Thoracic Society, ATS) to ascertain self-reported symptoms of chronic respiratory disease. Most analyses controlled for age, sex, previous smoking, occupational exposure to tobacco smoke, AOD before the age of 16 years, and education. Overall, study findings are informative, particularly because they focus on incident, rather than prevalent, respiratory disease. Study limitations include self-reporting of respiratory symptoms, varying specificity in measures of exposure, and coexposures to ozone and photochemical oxidants. The following paragraphs summarize a series of four reports about the incidence of respiratory outcomes covering various


PM10 and PM2.5 are notations for participate matter of less than 10 microns in diameter and less than 2.5 microns in diameter, respectively.


Criteria for definite chronic bronchitis required symptoms of cough or sputum on most days for at least 3 months/year, for 2 years or more. Criteria for definite asthma required a history of wheezing and a physician’s diagnosis of asthma. Asthma self-reporting was validated with information from medical charts.

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