Aerosols, Global Climate, and the Human Health Co-Benefits of Climate Change Mitigation - Aerosols: Measurement, Dosimetry, and Health Effects - page 348

that a pollution increase larger than 10 μg/m 3 , or the speciied increment, would be associated with
a proportionally larger increase in risk of health outcome.

13.3.2 l ong -t erM e xPosure e FFects oF PM
In addition to the health effects associated with acute exposure to PM pollution, long-term chronic
exposure to particles is also associated with increased lifetime risk of death, and has been estimated
to take years from the life expectancy of people living in the most polluted cities, relative to those
living in cleaner cities. The irst studies to show this association were cross-sectional studies that
compared metropolitan area death rates in high and low PM cities, after adjusting for potentially
confounding factors in the populations, such as age, sex, and race (Ozkaynak and Thurston, 1987).
These results have since been conirmed by cohort studies that followed large groups of individuals
in various cities over time that are able to control for potential confounding factors on an individual
level. For example, in the Six-Cities Study (that was a key basis for the setting of the USEPA's origi-
nal health-based regulation for a PM 2.5 annual standard in 1997), Dockery et al. (1993) analyzed
survival probabilities among 8111 adults living in six cities in the central and eastern portions of
the United States during the 1970 and 1980s. The cities were Portage, WI (P); Topeka, KS (T); a
section of St. Louis, MO (L); Steubenville, OH (S); Watertown, MA (M); and Kingston-Harriman,
TN (K). Air quality was averaged over the period of study in order to study long-term (chronic)
effects. It was found that the long-term risk of death, relative to the cleanest city, increased with ine
particle exposure, even after controlling for potentially confounding factors such as age, sex, race,
smoking, etc.
More recently, a study showed that long-term exposure to combustion-related ine particulate air
pollution is an important environmental risk factor for cardiopulmonary and lung cancer mortality
(see Figure 13.3). Indeed, this study indicates that the increase in risk of lung cancer from long-term
exposure to PM 2.5 was of roughly the same size as the increase in lung cancer risk of a nonsmoker
who breathes passive smoke while living with a smoker, or about a 20% increase in lung cancer risk
(Pope et al., 2002).
Other studies indicating health risk from chronic exposure to PM include a multicity U.S. study
inding than a 10 μg/m 3 increase in yearly PM 2.5 is associated with approximately an 11%-21%
increase in mortality (Eftim et al., 2008). A systematic review of research on long-term PM expo-
sure found that collectively, the studies indicate a 15%-21% increase in mortality per 10 μg/m 3
PM 2.5 (Chen et al., 2008).

1.2
1.1
1.0
0.9
0.8
0.7
0.6

1.2
1.1
1.0
0.9
0.8
0.7
0.6

All cause Cardiopulmonary

10 15 20 10 15 20

1.2 1.2

1.1
1.0
0.9
0.8
0.7
0.6

1.1
1.0
0.9
0.8
0.7
0.6

Lung cancer All other

10 15 20 10 15 20

µg/m 3 µg/m 3

FIGURE 13.3 Cardiac, lung, and cancer mortality risks of long-term ine PM exposure increase monotoni-
cally with exposure. (Adapted from Pope, C.A. et al., J. Am. Med. Assoc ., 287(9), 1132, 2002.)