Several epidemiologic studies have established a link between death rates and small airborne particles that are 2.5 microns in diameter or less, termed as PM2.5. In-depth studies are required to ascertain if improvements in particle exposure would mean greater survival rates.
Laden and her colleagues have explained in the American Journal of Respiratory and Critical Care Medicine, that from an earlier analysis of data from the Harvard Six Cities study, long-term exposure to air pollution particles causes high rates of mortality. The team analyzed data for 8 more years and during this period, air pollution was certainly lower in most of the cities undertaken for study. The areas that were part of their study was: Watertown, Massachusetts; Kingston and Harriman, Tennessee; St. Louis, Missouri; Steubenville, Ohio; Portage, Wyocena and Pardeeville, Wisconsin; and Topeka, Kansas.
True to the previous findings, it was observed that the mortality rate increased in those cities that recorded an increase in PM2.5 of 10 microgram per cubic meter. As PM2.5 levels dropped, the overall mortality rate also declined. The researchers were able to conclude that rise in mortality related to PM2.5 are "at least in part reversible."