Greater associations between risk of mortality and long-term exposures to relatively low concentrations of fine particulate matter (PM2.5) have been reported. Recognizing “more stringent air quality standards and guidelines will likely be considered,” The Health Effects Institute has funded three studies—in the United States, Europe and Canada—“to explore health effects from air pollution exposure at levels below government recommended standards.”
The four-year US study examined public data for 68.5 million older Americans and, in the low-exposure subcohort, focused on smaller towns and rural areas. Researchers reported increased risks of all-cause mortality with larger effect estimates in a low exposure subcohort. Stronger associations were found at exposure levels below the current US National Ambient Air Quality Standard (NAAQS) annual average exposure of 12 µg/m3. They also found stronger support for a likely causal effect between long-term exposure to PM2.5 and mortality. Results have become available as the Biden Administration and the US EPA are considering whether to strengthen the US EPA National Ambient Air Quality Standards for PM2.5.