Why Are Estimates of Attributable and Avoidable Health Events due to Exposure to Fine Particulate Sources Different?

Health benefits assessment from current exposure to fine particulate sources involves calculation of the number of Attributable adverse health events, while hypothetical future reductions in source‐specific exposure for the same population involve calculation of the number of Avoidable events. These two estimates can be very different depending on the shape of the relative risk function. We develop the mathematical justification for the calculation of Attributable and Avoidable events and characterize how they differ depending on the size of the source contribution and where on the relative risk curve exposure changes are being evaluated. The ratio of Attributable to Avoidable events is modeled as the ratio of the average derivative of the relative risk function over the total particulate mass range to the average derivative over the source‐specific mass range. This ratio can be greater or less than unity depending on the proportional size of the source to total mass and the curvature of the derivative. Relative risk functions at high global particulate concentrations can display little change in magnitude, resulting in ratios reaching into the hundreds. The difference between these estimates can be diminished if multiple particle sources are examined simultaneously. The use of highly non‐linear relative risk functions can pose risk communication challenges, with current estimates of health burden being very different than proposed improvements in air quality due to a reduction of a specific source for the same population. Widening the scope of health assessments to include multiple particulate sources can address these challenges.