A Novel Method Using Polyurethane Foam (PUF) Substrates to Determine Trace Element Concentrations in Size-Segregated Atmospheric Particulate Matter on Short Time Scales

A PUF-ICP-MS method has been developed that can quantify a large number of elements in size-resolved ambient aerosol samples collected over short-time intervals (four hours in this study). The pre-cleaning and digestion protocols developed enabled the quantification of 29 elements (including Hg) in ambient PM sampled onto a PUF substrate. The microwave-assisted acid digestion method affects a total dissolution of both aerosol and substrate, producing a colorless solution with no trace of aerosol, PUF, or polypropylene particulates, and is compatible with many analytical techniques (e.g., ICP-MS, CVAF, GFAA). For the large majority of elements the PUF-ICP-MS method provides superior elemental detection capabilities than traditional XRF approaches and importantly, method detection limits (MDLs) for most studied elements are lower than achieved with a 4-hour MOUDI approach using optimized ICP-MS analysis. For example, MDLs for V, Sr, Cd, Sb, and Hg are respectively 0.15, 0.18, 0.034, 0.051, and 0.0055 (solvent cleaning only for Hg) ng m−3. Only one-third, or less, of the PUF substrate is required for the ICP-MS analysis leaving the majority of the substrate available for additional characterization, e.g., organic speciation, of the same air mass. A demonstration study conducted in Phoenix, Arizona, shows that this new method can quantitatively resolve differences in element concentrations on short time scales and has the potential to be a powerful new tool for identifying sources of trace and ultra-trace elements. The highly size and time resolved data can also provide useful information for the study of health effects of individual or groups of elements.