Receptor modeling applied to patterns in space (RMAPS) .3. Apportionment of airborne particulate sulfur in western Washington state

Data obtained from 24 of the 31 sites of the Pacific Northwest Regional Visibility Experiment Using Natural Tracers (PREVENT) study were analyzed by the Receptor Model Applied to Patterns in Space (RMAPS) multivariate receptor model. Four spatial patterns were found and interpreted as showing the effect of the coal-fired power plant in Centralia, WA; transport from the northwest; the Seattle-Tacoma urban area; and transport from the southeast. In Mt. Rainier National Park, up to one-third of the sulfate can be attributed to the Centralia power plant. In the North Cascades National Park, 65-82% of the sulfur is accounted for by transport from Canada. The model was applied separately to sites in the northern and southern sections of the study area. The southern sites were affected only by the Centralia, urban, and southeast transport sources; the northern sites were affected only by the northwest transport, urban, and southeast transport sources. This gave two independent estimates of the normalized source contributions of the urban and southeast transport factors, which had a correlation coefficient of more than 0.90.