A New Method to Jointly Estimate the Mortality Risk of Long-Term Exposure to Fine Particulate Matter and its Components

Most studies on the association between exposure to fine particulate matter (PM 2.5 ) and mortality have considered only total concentration of PM 2.5 or individual components of PM 2.5 and not the combined effects of concentration and particulate composition. We sought to develop a method to estimate the risk of death from long-term exposure to PM 2.5 and the distribution of its components, namely: sulphate, nitrate, ammonium, organic mass, black carbon and mineral dust. We decomposed PM 2.5 exposure into the sum of total concentration and the proportion of each component. We estimated the risk of death due to exposure using a cohort of ~2.4 million Canadians who were followed for vital status over 16 years. Modelling the concentration of PM 2.5 with the distribution of the proportions of components together was a superior predictor for mortality than either total PM 2.5 concentration alone, or all component concentrations modelled together. Our new approach has the advantage of characterizing the toxicity of the atmosphere in its entirety. This is required to fully understand the health benefits associated with strategies to improve air quality that may result in complex changes not only in PM 2.5 concentration, but also in the distribution of particle components.