January 7, 2014 — Last month marked the 20th anniversary of the publication of Harvard School of Public Health’s groundbreaking Six Cities study, which—by revealing a strong link between air pollution and mortality risk—paved the way for strengthened U.S. regulations on fine particulate matter. Douglas Dockery—lead author of the Six Cities study and chair of HSPH’s Department of Environmental Health—answers three questions about the seminal study.
Q: What was the Six Cities study’s “aha” finding?
A: People in the dirtier cities were dying faster than people in the clean cities. We found that the mortality risk was strongly associated with fine particulate concentrations (particles smaller than 2.5 microns in diameter, or PM2.5). The differences we found in life expectancy—two to three years shorter—were remarkable. Those are big numbers in terms of population life expectancy. We were astonished that people in the clean cities were living that much longer, just because of where they lived. The “dirty” communities were all within air pollution standards at the time—they weren’t defined as being “unhealthy” by the Environmental Protection Agency (EPA)—but the Six Cities Study strongly suggested negative health effects in those communities.
Q: What have been the long-term health benefits resulting from the study?
A: New standards put in place by the EPA following the study have led to an improvement in air quality, with PM2.5 concentrations going down consistently over the past 20 years. We have evidence that this has led to improved health in follow-up studies. We saw improvements in health in each of the six cities—even in our “clean” cities—consistent with the improvement in air quality. There’s an important message here: Any improvement in air quality and reduction in particle concentrations leads to improved health. In 2009 we examined changes in life expectancy and changes in PM2.5 air pollution in 211 counties in the U.S. between 1980 and 2000. We found that average life expectancy has increased—by roughly 2.7 years—and that declining air pollution was likely responsible for about 0.8 years of that increase. In 2011 the EPA estimated that the control of particulate air pollution saved 160,000 lives in 2010, and that it will save 230,000 lives in 2020.
Q: What have been the long-term economic benefits resulting from the study?
A: When the federal Office of Management and Budget evaluated for Congress the benefits and costs of all federal regulations in 2007, they found the largest estimated benefit was from reduction in air pollution from a single air pollutant: fine particulate matter. The benefits were estimated at between $18.8 billion and $167.4 billion per year, compared to a cost of $7.3 billion per year. That translates to a benefit-cost ratio of between 2.5 to 1 or possibly up to 20 to 1. These are pretty astounding numbers for the benefits that were initiated by the 1993 Six Cities Study publication. That specific study ultimately led to a new agenda for air pollution research, new air quality standards, improved air quality, and evidence of the benefits of cleaner air.