Estimating aerosol surface area from number and mass concentration measurements.

Andrew Maynard

doi:10.1093/annhyg/meg022

Abstract

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.

Highlights

A number of studies in recent years have demonstrated that response to inhaled low-solubility particles is highly dependent on particle size (Oberdörster et al, 1995; Oberdörster, 2000; Brown et al, 2001)
= geometric standard deviation = estimated σg of an assumed lognormal distribution = total concentration of quantity i = median diameter associated with quantity i = minimization function = particle density
NUMBER AND MASS CONCENTRATION MEASUREMENTS. These iterative calculations have been written in Excel (Microsoft, USA), but can be adapted for most spreadsheet applications

Summary

INTRODUCTION

A number of studies in recent years have demonstrated that response to inhaled low-solubility particles is highly dependent on particle size (Oberdörster et al, 1995; Oberdörster, 2000; Brown et al, 2001). Validation of this hypothesis requires extensive data relating health effects to aerosol surface area within the workplace. Aerosol surface area characterization methods are at a relatively early stage of development, and appropriate instrumentation for routine workplace exposure measurements is not generally available. An impasse exists where the development of instrumentation necessary for exploring how occupational health is associated with aerosol surface area is itself dependent on the very information it will be used to obtain. It is of considerable interest to consider whether such measurements could be used to estimate aerosol surface area concentration. In this paper the theoretical use of aerosol number and mass concentration measurements to estimate surface area is considered, and errors associated with characterizing a range of aerosol size distributions examined

BACKGROUND

DISCUSSION

SUMMARY