1 CHAPTER 2- Air Quality and Human Health

• A substantial body of epidemiological evidence now exists that establishes a link between exposure to air pollution, especially airborne particulate matter, and increased mortality and morbidity, including a wide range of adverse cardiorespiratory health outcomes. Many time-series studies, conducted throughout the world, relate day to day variation in air pollution to health with remarkable consistency. A smaller number of longer-term cohort studies find that air pollution increases risk for mortality. • Health effects are evident at current levels of exposure, and there is little evidence to indicate a threshold concentration below which air pollution has no effect on population health. • It is estimated that the shortening of life expectancy of the average population associated with long-term exposure to particulate matter is 1-2 years. • Recent epidemiological studies show more consistent evidence of lung cancer effects related to chronic exposures than found previously. • In general, methodologic problems with exposure classification tend to diminish the risks observed in epidemiological studies so that the true risks may be greater than observed. • Human clinical and animal experimental studies have identified a number of plausible mechanisti