Air quality data accumulated since 1965 indicate the primary and secondary national air quality standards have been exceeded in the Duwamish Basin area of Seattle, Washington. The objective of the study was to determine the nature of suspended particulate and subsequently to quantify the impact of particulate sources. Ambient and source particulate was collected on fiberglass and membrane filters. Results from gravimetric, elemental, and compound analyses were combined with meteorological data for correlation and analyses. The contribution of sources for the basin was found to be 27 percent from natural sources, 39 percent transportation, and 34 percent point industry and multiple-area sources. Results from the study show the complexity of suspended particulate. Source tests showed a multitude of elements and compounds present and, to complicate matters, surrounding soil has been contaminated by industrial and area sources. About 35 percent of the particulate is directly related to road dust-type emissions.