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Populations at Risk from Particulate Air Pollution -- United States, 1992

Despite improvements in air quality since the 1970s, air pollution remains an important environmental risk to human health. A national health objective for the year 2000 is to reduce exposure to air pollutants so that at least 85% of persons live in counties that meet U.S. Environmental Protection Agency (EPA) standards (objective 11.5) (1). This report provides estimates from the American Lung Association (ALA) of populations potentially at risk from exposure to particulate air pollution in the United States during 1992.

The National Ambient Air Quality Standard for particulate matter less than 10 um in diameter (PM10) is 150 ug/m(3), averaged over 24 hours (2). The federal standard is met if this value is not exceeded more than once per calendar year, and the annual arithmetic mean is less than or equal to 50 ug/m(3). Information in this report is based on the second highest maximum 24-hour PM10 concentrations recorded by at least one monitor in 1992 (EPA, unpublished data, 1993). Both the federal "exceedance" definition (greater than or equal to 155 ug/m(3)) and a similar approach applied to the California standard * (greater than or equal to 55 ug/m(3)) were used as cutoff values. Estimates of the numbers of persons potentially exposed to levels of PM10 above these cutoff values were derived from 1991 census figures for each county (U.S. Bureau of the Census, unpublished data, 1992).

For this report, a population at risk was defined as persons who have a "significantly higher probability of developing a condition, illness, or other abnormal status," as described by EPA (4). Five at-risk populations were included: preadolescent children (aged less than or equal to 13 years), the elderly (aged greater than or equal to 65 years), persons aged less than 18 years with asthma, adults (aged greater than or equal to 18 years) with asthma, and persons with chronic obstructive pulmonary disease (COPD) (e.g., chronic bronchitis and emphysema). Age-specific county populations for 1991 were estimated by applying the population age distribution of each state (U.S. Bureau of the Census, unpublished data, 1992) to the counties within that state. The number of persons with asthma or COPD in each county was estimated by applying age-specific prevalences from CDC's National Health Interview Survey (5) to age-specific population estimates for each county. Although PM10 levels are presented on a county basis, they do not indicate that all areas of the county were subject to that level or that all persons in the county were exposed to the recorded concentration.

During 1992, PM10 levels were greater than or equal to 155 ug/m(3) in 16 counties; an estimated 23 million persons (9.1% of the total U.S. population) resided in these counties (Table_1). Approximately 92 million additional persons (36% of the U.S. population) resided in counties in which PM10 levels were 55 ug/m(3)-154 ug/m(3). Overall, an estimated 115 million persons (45% of the U.S. population) resided in counties with PM10 levels greater than or equal to 55 ug/m(3) (Table_1). In the United States during 1992, 46% of persons with asthma lived in communities with levels of particulate air pollution higher than the California standard.

Reported by: P Vigliarolo, Communications Div; S Rappaport, MPH, K Lieber, MPH, A Gorman, Epidemiology and Statistics Div; R White, MST, National Programs Div, American Lung Association, New York. Air Pollution and Respiratory Health Br, Div of Environmental Hazards and Health Effects, National Center for Environmental Health, CDC.

Editorial Note

Editorial Note: Particulate matter (e.g., dust, dirt, and smoke) is a complex and varying mixture of substances. Sources include motor-vehicle emissions, factory and utility smokestacks, residential wood burning, construction activity, mining, agricultural tilling, open burning, wind-blown dust, and fire. Some particles are formed in the atmosphere through the condensation or transformation of other chemical substances. Particles with diameters less than 10 um pose a greater health risk than larger particles because particles of this size are easily inhaled deep into the lungs.

Increased risks for illness and death have been associated with particulate air pollution at levels comparable to those presented in this report (6-8). Acute effects on the respiratory system are well established and include exacerbations of chronic respiratory disease, restrictions in activity, and increases in emergency department visits and hospitalizations for respiratory illness (8). Persons with asthma are particularly sensitive to the effects of particulate air pollution (8). A national health objective for the year 2000 is to reduce asthma morbidity, measured by a reduction in asthma hospitalizations, from 188 per 100,000 in 1987 to no more than 160 per 100,000 (objective 11.1) (1).

The estimates presented in this report underscore the potential public health importance of particulate air pollution. Although levels of airborne particulate pollution declined substantially from 1988 to 1992 (emissions of PM10 decreased 8% and air concentrations of PM10 decreased 17%) (9), continued efforts are required to reduce health risks associated with particulate air pollution. EPA is reviewing technical and scientific information to determine whether the federal ambient air quality standard for particulate matter, established in 1987, should be revised.

ALA recently issued The Perils of Particulates (10), which includes national and county estimates of populations at potential risk for exposure to particulate air pollution. Copies are available from local offices of the ALA, telephone (800) 586-4872.


  1. Public Health Service. Healthy people 2000: national health promotion and disease prevention objectives. Washington, DC: US Department of Health and Human Services, Public Health Service, 1991; DHHS publication no. (PHS)91-50213.

  2. US Environmental Protection Agency. Revisions to the National Ambient Air Quality Standard for particulate matter: final rule. Federal Register 1987;52:24634.

  3. Air Resources Board. California ambient air quality standard for particulate matter (PM10). Sacramento, California: State of California, Air Resources Board, Research Division, December 1982.

  4. US Environmental Protection Agency. Air quality criteria document for lead. Washington, DC: US Environmental Protection Agency, 1977.

  5. NCHS. Current estimates from the National Health Interview Survey, 1991. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1992; DHHS publication no. (PHS)92-1509. (Vital and health statistics; series 10, no. 184).

  6. Ostro B. The association of air pollution and mortality: examining the case for inference. Arch Environ Health 1993;48:336-

  7. Schwartz J. Air pollution and daily mortality: a review and meta analysis. Environ Res 1994;64:36-52.

  8. Dockery DW, Pope CA. Acute respiratory effects of particulate air pollution. Annu Rev Public Health 1994;15:107-32.

  9. Curran T, Faoro R, Fitz-Simons T, et al. National air quality and emissions trends report. Research Triangle Park, North Carolina: US Environmental Protection Agency, Office of Air Quality Planning and Standards, October 1993; publication no. EPA-454/R-93/031.

  10. American Lung Association. The perils of particulates: an estimation of populations at risk of adverse health consequences from particulate matter in areas with particulate matter levels above the National Ambient Air Quality Standards (NAAQS) of the Clean Air Act and the state of California's air quality standard. New York: American Lung Association, 1994.

* California's particulate matter air quality standard of 50 ug/m(3) averaged over 24 hours (3) is the most stringent standard in the United States.
Note: To print large tables and graphs users may have to change their printer settings to landscape and use a small font size.

TABLE 1. Estimated number and percentage of the total population and at-risk * subgroups residing in
counties with particulate air pollution with a diameter of <10 um (PM10) at levels >=155 ug/m(3) and
>=55 ug/m(3) + -- United States, 1992 &
                                       PM10 levels >=155 ug/m(3)         PM10 levels >=55 ug/m(3)
                                       -------------------------         ------------------------
Population at risk                         No.            (%) @              No.           (%) @
Total population                       22,894,856         (9.1)          114,671,632       (45.5)

Preadolescent children
  (aged <=13 yrs)                       4,931,408         (9.5)           23,794,139       (46.0)
Elderly (aged >=65 yrs)                 2,649,477         (8.3)           14,010,297       (44.1)
Persons (aged <18 yrs)
  with asthma                             387,220         (9.5)            1,878,848       (45.9)
Persons (aged >=18 yrs)
  with asthma                             697,444         (9.1)            3,528,475       (46.2)
Persons with chronic
  obstructive pulmonary
  disease **                            1,243,407         (9.1)            6,263,409       (46.0)
 * Population-at-risk estimates should not be added to form totals. These categories are not mutually
 + PM10 >=155 ug/m(3) is the federal "exceedance" definition; PM10 >=55 ug/m(3) is the California
   "exceedance" standard.
 & The PM10 level of the county does not imply responsibility for the disease status of its
 @ Of the total population in the category, the proportion of each population subgroup potentially
** Includes chronic bronchitis and emphysema.

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