Estimating aerosol surface area from number and mass concentration measurements

A number of toxicology studies have been published indicating that health effects associated with low-solubility inhaled particles may be more appropriately associated with particulate surface area than mass. While exposure data from the workplace is needed to further investigate the relevance of such an association, the means of measuring exposure to aerosol surface area are not readily available. A possible interim solution is to estimate surface area from measurements of particle number and mass concentration using readily available direct-reading instruments. By assuming a lognormal aerosol size distribution with a specific geometric standard deviation, number and mass concentration measurements may be used to estimate the surface area concentration associated with the distribution. Simulations have shown that surface area estimates made on unimodal lognormal aerosols will frequently lie within 100% of the actual value. Simulations using bimodal distributions indicate estimates of surface area vary from the actual value by less than an order of magnitude. Calculations based on experimental unimodal and bimodal data confirm these findings, with estimated surface area rarely being a factor of 4 greater than the actual value, and frequently being much closer than this. These findings indicate that estimating aerosol surface area exposure using readily available number and mass concentration direct-reading instruments may be suitable for providing initial data on the magnitude of surface area exposures with minimal additional effort. This would allow the accumulation of valuable exposure-response data prior to the development and implementation of more sophisticated instrumentation to more accurately estimate surface area exposure.