Over a dozen studies have found significant associations between various measures of long-term exposure to PM and elevated rates of annual mortality (e.g.
Studies have found associations between long term exposure to PM and elevated rates of mortality. 
mnli hypothesis: Studies have found associations between long term exposure to PM and elevated rates of mortality.  premise: Over a dozen studies have found significant associations between various measures of long-term exposure to PM and elevated rates of annual mortality (e.g.