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Water-soluble redox-active metals are potentially toxic due to its abilityto catalytically generate reactive oxygen species (ROS) in vivo, leading tooxidative stress. As part of the Southeastern Center for Air Pollution andEpidemiology (SCAPE), we developed a method to quantify water-solubleelements, including redox-active metals, from a large number of filtersamples (N = 530) in support of the center's health studies. PM2.5samples were collected during 2012–2013 at various sites (three urban, tworural, a near-road site, and a road-side site) in the southeastern United States,using high-volume samplers. Water-soluble elements (S, K, Ca, Ti, Mn, Fe,Cu, Zn, As, Se, Br, Sr, Ba, and Pb) were determined by extracting filters indeionized water and re-aerosolized for analyses by X-ray fluorescence (XRF)using an online aerosol element analyzer (Xact, Cooper Environmental).Concentrations ranged from detection limits (nominally 0.1 to 30 ng m−3)to 1.2 μg m−3, with S as the most abundant element, followed byCa, K, Fe, Cu, Zn, and Ba. Positive matrix factorization (PMF) identifiedfour factors that were associated with specific sources based on relativeloadings of various tracers. These include brake/tire wear (with tracers Baand Cu), biomass burning (K), secondary formation (S, Se, and WSOC), andmineral dust (Ca). Of the four potentially toxic and relatively abundantmetals (redox-active Cu, Mn, Fe, and redox-inactive Zn), 51 % of Cu,32 % of Fe, 17 % of Mn, and 45 % of Zn were associated with thebrake/tire factor. Mn was mostly associated with the mineral dust factor(45 %). Zn was found in a mixture of factors, with 26 % associated withmineral dust, 14 % biomass burning, and 13 % secondary formation.Roughly 50 % of Fe and 40 % of Cu were apportioned to the secondaryformation factor, likely through increases in the soluble fraction of theseelements by sulfur-driven aerosol water and acidity. Linkages betweensulfate and water-soluble Fe and Cu may account for some of the pastobserved associations between sulfate/sulfur oxide and health outcomes. ForCu, Mn, Fe, and Zn, only Fe was correlated with PM2.5 mass (r =0.73–0.80). Overall, mobile source emissions generated through mechanicalprocesses (re-entrained road dust, tire and break wear) and processing bysecondary sulfate were major contributors to water-soluble metals known tobe capable of generating ROS

atmospheric chemistry and physics

PM&amp;lt;sub&amp;gt;2.5&amp;lt;/sub&amp;gt; water-soluble elements in the southeastern United States: automated analytical method development, spatiotemporal distributions, source apportionment, and implications for heath studies