1. A method to determine regional sources of pollution aerosol which includes: (a) selecting empirically a small number of suitable tracer elements which are pollution-derived, associated with submicron-sized particles, and accurately analyzable in the aerosol; (b) measuring the concentrations of each tracer element in multiple samples of regionally-representative aerosol at multiple sites in each source region whose signature is to be determined; (c) expressing the measured results as ratios to one of the tracer elements; (d) defining the elemental signature of the source region as the collection of elemental ratios and associated standard deviations which best represents that region's aerosol; (e) determining the source region's signature from modes in the logarithmic frequency distributions of the elemental ratios of samples taken in source region; (f) measuring the concentrations of each tracer element in multiple samples of an aerosol from a receptor region; (g) comparing the elemental ratios from the receptor region to the signatures from possible source regions to determine the most probable source region.