A growing number of studies have produced results that suggest the shape of the concentration-response (C-R) relationship between PM2.5 exposure and mortality is “supralinear,” such that incremental risk is higher at the lowest exposure levels than at the highest exposure levels. If the C-R relationship is in fact supralinear, there may be significant health benefits associated with reductions in PM2.5 below the current US National Ambient Air Quality Standards (NAAQS), as each incremental tightening of the PM2.5 NAAQS would be expected to produce ever-greater reductions in mortality risk.

Director Garrett Glasgow, Senior Consultant Bharat Ramkrishnan, and Affiliated Consultant Anne E. Smith were commissioned by the Electric Power Research Institute (EPRI) to perform a numerical simulation study to test whether there are conditions that could produce apparent supralinearity when the true PM2.5 C-R relationship is linear.

Their study demonstrates the difficulty of developing a clear understanding about the shape of the C-R relationship between long-term PM2.5 exposure and health risk without first resolving uncertainties regarding differential toxicity in types of PM2.5, correlated risk factors, and geographic variation in exposure measurement error. This in turn has clear implications for policymakers considering evidence of supralinear C-R relationships when determining appropriate air quality standards.