Toxic Metal Particulates in Chicago Air and in Mercury-Water-Organic Solutions

In this thesis, toxic metal particulates were analyzed in urban air and a model aqueous environment. In Chapter 2, particulates with diameters of >2.5 μm (large), ≤2.5 μm to >1.2 μm (medium), and ≤1.2 μm to >0.3 μm (small) were collected in Chicago summertime air from 2018-2021 and analyzed for toxic metals. Common particulate sources were iron and steel works, cement and construction/demolition, fireworks, road dust, coal burning, and nonferrous metal plating/processing. Sources shifted in importance from year to year. In Chapter 3, particulate-bound mercury (PBM) concentrations were examined over all seasons from 2018-2021 in the same three particle size fractions at the same UIC site. Local sources, such as ferrous and nonferrous metals processing, coal burning, cement production, construction/demolition, traffic, and gaseous elemental mercury oxidation as well as distant sources such as wildfires influenced PBM concentrations. These sources shift in importance with season and year. In Chapter 4, solid HgS products produced by the reaction of Hg(II) and a highly reactive organosulfur compound in the presence of ambient air at multiple combinations of pH and S:Hg ratios in aqueous solutions were speciated by HR-XANES spectroscopy and quantified by unconstrained linear least-squares fitting to reference spectra. Reaction products formed on the order of minutes and included metastable nanoparticulate and well-crystallized metacinnabar (β-HgS) as well as the stable cinnabar (α-HgS). The results of this dissertation may help inform decisions about public health and air quality in urban environments and help determine the fate and transport of toxic metals through the atmosphere and aquatic systems.