This project involves the analysis and modeling of individual urban atmospheric dust particles using scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), focused ion-beam (FIB) tomography, 3-D reconstructions of the particles, and the discrete dipole approximation method for calculating particle optical properties. The particles are heterogeneous in that they have multiple chemical phases. The collected data sets are: 1) element concentrations for selected particles from filter samples using SEM-EDX, 2) element spatial maps of particles using SEM-EDX, 3) secondary electron images from SEM, 4) text files containing information on the locations of chemical phases for each particle based on 3-D reconstructions from FIB tomography, and 5) optical property calculations of particles using the DDA program DDSCAT.