Windblown dust contributes to high PM2.5 concentrations

The revised National Ambient Air Quality Standards for PM include fine particulate standards based upon mass measurements of PM2.5. It is possible in arid and semi-arid regions to observe significant coarse mode intrusion in the PM2.5, measurement. In this work, continuous PM10 PM2.5 and PM1.0 were measured during several windblown dust events in Spokane, WA. PM2.5 constituted similar to 30% of the PM10 during the dust event days, compared with similar to 48% on the non-dusty days preceding the dust events. Both PM10 and PM2.5 were enhanced during the dust events. However, PM1.0, was not enhanced during dust storms that originated within the state of Washington. During a dust storm that originated in Asia and impacted Spokane, PM1.0 was also enhanced, although the Asian dust reached Washington during a period of stagnation and poor dispersion, so that local sources were also contributing to high particulate levels. The "intermodal" region of PM, defined as particles ranging in aerodynamic size from 1.0 to 2.5 mu m, was found to represent a significant fraction of PM2.5 (similar to 51%) during windblown dust events, compared with 28% during the non-dusty days before the dust events.