A derived association between ambient aerosol surface area and excess mortality using historic time series data

Although aerosol mass concentration is widely associated with ill health following inhalation; there is increasing evidence that it is a poor indicator of fine and ultrafine particle toxicity. Research has indicated that biological response to such particles is closely associated with particulate surface area; although no epidemiology data currently exist to validate the association. By applying a simple model to historic mass-based time series data, we have been able to estimate mortality rate as a function of ambient aerosol surface area. Within the simplifying assumptions of the model, a linear association is indicated between mortality rate and surface area concentration for coalescing particles. The analysis also indicates the existence of a threshold aerosol concentration, below which particulate mass and surface area are linearly related. Below this threshold, we suggest that mass concentration measurements may provide a good indicator of health effects, although for high exposures found in the developing world and industry, the model indicates that aerosol exposure may be more appropriately characterized by surface area. Further experimental validation of the model should establish the applicability of derived relationships between aerosol mass and surface area concentration to ambient and occupational exposures.