Qian Di, et al. - Researchers aspired to evaluate the association between short-term exposures to ambient fine particulate matter (PM_2.5) and ozone, and at levels below the current daily National Ambient Air Quality Standards (NAAQS), and mortality in the continental United States. Short-term exposures to PM2.5 and warm-season ozone were significantly correlated with increased risk of mortality in the US Medicare population from 2000 to 2012. This risk occurred at levels below current national air quality standards, implying that these standards would need to be reevaluated.