Understanding the joint impacts of fine particulate matter concentration and composition on the incidence and mortality of cardiovascular disease: a component-adjusted approach

Past health impact assessments of ambient fine particles (PM_2.5) have generally considered mass concentration only, despite PM_2.5 is a heterogeneous mixture. Given constant changes in the concentration and composition of atmospheric aerosol, considerable uncertainty exists as to whether the current focus on PM2.5 mass or individual components may fully characterize the health burden of PM_2.5. We proposed a component-adjusted method that jointly estimates the health impacts of PM_2.5 and its major components while allowing for a potential nonlinear PM_2.5-outcome relationship. Using this method, we quantified the effects of PM_2.5 on the risks of developing acute myocardial infarction (AMI) and dying from cardiovascular causes in comparison to three traditional approaches in the entire adult population across Ontario, Canada. We observed that PM_2.5 was positively associated with AMI incidence and cardiovascular mortality with all four methods. Comparing to the traditional approaches, however, the new component-adjusted approach demonstrated a significant improvement in explaining the health impacts of PM_2.5, especially in the presence of a nonlinear PM_2.5-outcome relationship. Using the new approach, we found that the effects of PM_2.5 on AMI incidence and cardiovascular mortality may be on average 10% to 27% higher than what would be estimated from the conventional approaches examining PM_2.5 alone.