Conversion of Multicomponent Aerosol Size Distributions from Sectional to Modal Representations

Abstract

A new method for converting a multicomponent aerosol size distribution from sectional to modal form is presented. The sectional distribution is fit with multiple lognormal modes using a nonlinear least-square regression that considers both the overall mass distribution and individual component distributions. The new method is compared to other conversion methods that assign sections to modes arbitrarily or that fit only the total mass distribution. Results of conversion tests using example distributions show that the multicomponent fit method is able to define a modal distribution that more accurately represents the original sectional distribution than do other methods. Total and component mass are conserved, the size, shape, and location of peaks match the original distribution, and modal compositions allocate components to the same size range as in the sectional representation. It is also able to convert distributions with relatively few size sections or where the size sections do not span the entire distribution, and it does not propagate errors when distributions are converted repeatedly between sections and modes.