Determining the trace element content of inhalable airborne particles is of vital importance because they cause cardiovascular and pulmonary diseases and damage the environment. Of particular relevance to this research is that crude oil cracking catalysts are strongly enriched in light lanthanoids to impart hydrothermal stability and increase activity, selectivity and gasoline yield. Also, 21 tons of lanthanoids is estimated to be lost daily by refineries in the United States through atmospheric emission, incorporation into products, and removal for disposal at landfills. Since petroleum refining is an important activity in Texas’ Gulf coast we hypothesized that atmospheric emissions from fluidized-bed catalytic cracking units modifies rare earth element (REE) composition of aerosols in Houston, TX compared with their crustal values. Consequently, we determine REE relative abundance sequences, ratios of La to light REEs (Ce, Pr, Nd, and Sm), and enrichment factors to provide evidence that petrochemical cat cracking operations are predominantly responsible for REE enrichment in ambient airborne particles in Houston. By analyzing REEs, we also track episodic (i.e. upset) emissions from cat cracking units of a local refinery to a site approximately 40 km downwind, illustrating the strength of the analytical method to isolate an important source during a regional haze episode not related to the emission event. REE concentrations during the episode were up to 200-fold higher than background levels, demonstrating significant episodic enrichment. We also demonstrate that REE measurements can isolate long-range transport of Saharan dust (i.e. crustal material) and quantify its effects on composition and mass concentrations of ambient airborne particulate matter. This presentation will conclude by showing several lines of evidence including receptor modeling, lanthanoid ratios, and La-Ce-Sm ternary diagrams that prove infiltration/ventilation of outdoor aerosols emanating from petroleum refineries as being largely responsible for enhanced La and total lanthanoid concentrations inside a high school located in the proximity of refineries. In conclusion, we prove the inherent value of REE measurements to developing air quality management strategies and recommend continuous independent monitoring of emissions to augment existing industry self-reporting regulatory requirements in urban areas in the vicinity of petroleum refineries.

Atmospheric chemistry of lanthanoids in Houston, Texas: Quantifying rare earths to apportion petroleum refining and African dust impacts on ambient airborne particulate matter

2019 Spring National Meeting

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