Source Identification on High PM2.5 Days using SEM/EDS, XRF, Raman, and Windblown Dust Modeling

When community exposures to PM2.5 are high, identification of the particle sources enables more effective control and assessment of health impacts. This study demonstrates forensic particle analysis methods that can be used when only limited, archived samples are available. Federal reference method (FRM) filters from seven high PM2.5 days were analyzed using optical and electron microscopy, X-ray fluorescence, and Raman micro-spectroscopy to determine individual particle morphology and composition, together with supplemental wind roses, GIS mapping, FRM inlet penetration calculations, and windblown dust modeling. This approach identified three distinct sources of high PM2.5 measurements: 1) local, windblown dust from an atypical direction, consistent with modeling predictions for a normally operating PM2.5 inlet challenged with a high concentration of windblown dust particles, potentially enhanced by re-entrainment of particles from within the inlet, 2) wintertime, regional, hygroscopic, nitrogen- and sulfur-rich salts, consistent with ammonium nitrate and ammonium sulfate, and 3) sampling or documentation error. This approach can be used in any location in which regulatory PM filters and other air quality data are available.