BOSTON — Harvard University scientists say they’ve found a link between people living longer and cities reducing the amount of fine particulate matter in the air. Lead author Francine Laden, an assistant professor of environmental epidemiology, said the eight-year follow-up to the landmark Harvard Six Cities Study found the largest drops in mortality rates were in cities with the greatest reduction in fine particulate air pollution. The findings remained valid after controlling for the general increase in adult life expectancy in the United States during both the original and follow-up study periods. The original Harvard Six Cities Study evaluated the effects of pollution on adults during the 1970s and 1980s. The results showed a strong, positive correlation between levels of air pollution and mortality — and the study led to a revision of existing air quality standards by the Environmental Protection Agency. The follow-up study population consisted of nearly 8,100 white participants residing in Watertown, Mass.; Kingston and Harriman, Tenn.; St. Louis, Mo.; Steubenville, Ohio; Portage, Wyocena and Pardeeville, Wis.; and Topeka, Kan. The most recent study was published in the March 15 issue of the American Journal of Respiratory and Critical Care Medicine.