Developing parameters for local multimode ambient aerosol models including nanometer mode

The particle count, surface and mass in an occupied space can be modeled when the outdoor and recirculation airflows are known, along with the particle-size distribution for outdoor air, internal generation rates as a function of particle size, and the efficiency of the filter system as a function of particle size. Data on outdoor air particle-size distribution is rarely available, but two measures of particle mass concentration, PM2.5 and PM10, are often available for both urban and rural locations. Many studies have shown that outdoor air aerosol size distributions are well modelled by sums of two or three log-normal distributions, with essentially all the mass contained in the two larger modes, the accumulation mode and the coarse mode. Other studies have also shown that the geometric mean diameter and standard deviations of the accumulation and coarse modes are, in general, related by simple functions. This paper shows how these relationships can be combined with the known characteristics of PM2.5 and PM10 samplers to create reasonable models of outdoor air aerosol-size distributions, and thus allow calculation of aerosol mass effects in occupied spaces. Means of estimating the parameters of aerosol modes with mean sizes below 100 nm and the efficiencies of filters in that range are described. These estimates allow extension of indoor-air modeling to include aerosol surface, which is predominately due to particles with diameters below 100 nm. Sources of the necessary data for all size ranges are examined.