Measurement of the Trace Element Composition of Airborne Particulate Matter and its Use in Source Apportionment: Case Studies of Lanthanoids and Platinum Group Metals from Houston, Texas
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2015 American Chemical Society. We demonstrate that the composition and abundance sequence for many elements in airborne particles in an urban/industrial environment (i.e. Houston, TX) differs substantially from their average crustal values due to the influence of local anthropogenic sources. Evidence is also provided for the long-range transport of desert dust (i.e. crustal material) and its effects on composition and mass concentrations of ambient particulate matter in Houston using detailed elemental analysis. Lanthanoid metals and platinum group elements (PGEs) are shown to be excellent markers for primary emissions from catalytic cracking operations during petroleum refining and gasoline-driven light-duty vehicles, respectively. Therefore, systematic measurement of numerous representative, transition, and rare earth elements will assist in identifying and apportioning various anthropogenic and natural aerosol sources. Underlying such research are accurate and precise analytical methods to digest airborne particulate matter and quantify trace to major levels of a wide range of elements necessary for robust source apportionment. Our sample preparation procedures and inductively coupled plasma - mass spectrometry techniques for elemental analysis including lanthanoids, rhodium, palladium, and platinum are summarized. We use elemental abundance profiles and concentration ratios of specific tracer elements, focusing on lanthanoids and PGEs, to track locally emitted and long-range transported aerosols. Finally we list possible sources and their individual contributions to ambient particulate matter (PM) derived from source apportionment studies based on elemental characterization of ambient aerosols at receptor locations.
