Detection and Characterization of Size- and Time-Resolved Particulate Matter Using Enhanced Optical and Elemental Analyses: Implications for Anthropogenic Source Identification in the Houston Ship Channel Area
Spada, Nicholas James
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Methods were developed for the accurate measurement of optical and elemental properties of particulate matter samples, with an emphasis on size- and time-resolved samples. These techniques were applied to environmental samples collected near the Houston ship channel and in the Washburn Tunnel. First, optical extinction was quantified using a modified integrating plate method for samples presorted into eight size bins ranging from coarse (10-5.0 μm) to the Aitken size mode (0.26-0.09 μm). Depending on mass loading, expected time resolution for typical urban environments could be one hour. Calibrations using resuspended non-absorbing salts and carbon particles revealed an anomaly unique to particles between 0.56 and 0.75 μm equivalent diameter. These results may provide evidence of particle deagglomeration, which would significantly alter size-dependent correction factors used in mass and X-ray fluorescence analyses of samples collected by virtual impactors. Next, a robust method for detecting platinum group elements along with 42 main group and rare earth elements was generated for road dust samples collected in the Washburn Tunnel. The successful application of this method resulted in > 90% recovery of platinum group elements after removal of isobaric interferences and polyatomic species arising from other anthropogenically emitted metals. Characterizations of road dusts collected in the Washburn Tunnel as well as from surrounding areas underscored the isolation of the Washburn Tunnel environment from outside sources. Additionally, interpretation of the elemental signatures of tunnel road dusts exposed stark contrasts to historical standards of autocatalyst material and European observations. Finally, a multi-site study surrounding the Houston ship channel was conducted in the fall of 2012. The size- and time-resolved particulate matter samples were analyzed using the newly developed optical and elemental methods. Results indicated a complete lack of temporal correlation between measured size bins, with anthropogenic emission events typically lasting between two and six hours. With the combination of meteorological data, multiple pollutant sources, including marine vessel and petrochemical manufacturing facilities, were uniquely identified in separate size bins. These findings highlighted the need for size- and time-resolved monitoring of trace elements in urban/industrial environments to better understand links between aerosolized transition metals and human health effects.