Improved source apportionment and speciation of low-volume particulate matter samples

New chemical analysis methods for the characterization of atmospheric particulate matter (PM)* samples were developed and demonstrated in order to expand the number of such methods for use in future health studies involving PM. Three sets of methods were, developed, for the analysis (1) of organic tracer compounds in low-volume personal exposure samples (for source apportionment), (2) of trace metals and other trace elements in low-volume personal exposure samples, and (3) of the speciation of the oxidation states of water-soluble iron (Fe), manganese (Mn), and chromium (Cr) in PM samples. The development of the second set of methods built on previous work by the project team, which had in the past used similar methods in atmospheric source apportionment studies. The principal challenges in adapting these methods to the analysis of personal exposure samples were the improvement of detection limits (DLs) and control of the low-level contamination that can compromise personal exposure samples. A secondary goal of our development efforts was to reduce the cost and complexity of the three sets of methods in order to help facilitate their broader use in future health studies. The goals of the project were achieved, and the ability to integrate the methods into existing health studies was demonstrated by way of conducting two pilot studies. The first study involved analysis of trace elements in size-resolved PM samples that had been collected to represent study subjects' personal exposures along with simultaneous measures of indoor and outdoor PM concentrations. The second study involved analysis of the speciation of organic tracer compounds in personal exposure samples, indoor samples, and outdoor samples in order to understand the diesel PM exposure of study subjects in various job classifications in an occupational setting. Both pilot studies used existing samples from. large multi-year health studies and were intended to demonstrate the feasibility and value of using the new chemical analysis methods to better characterize the personal exposure samples. Analysis of the health data and the broader implications of the exposure assessments were not evaluated as part of the present study, but our pilot-study measurements are expected to contribute to investigators' future analyses in the large multi-year health studies. The methods we developed for the low-cost measurement of the oxidation states of Fe, Mn, and Cr in atmospheric PM samples are extremely sensitive and well suited for use in health studies. To demonstrate the utility of these methods, small-scale studies were conducted to characterize the redox cycling of Fe in PM on the time scale of atmospheric transport from source to personal exposure and to provide preliminary data on the atmospheric concentrations of soluble forms of the target metals in selected urban environments (in order to help focus future research seeking to understand the role of metals in human exposure to PM and its adverse health effects). The present report summarizes the methods that were developed and demonstrated to be suitable for use in health studies and provides pilot-scale data that can be used to develop hypotheses and experimental strategies to further enhance the ability of future health studies to elucidate the role of PM, PM sources, and PM components in the observed associations between atmospheric PM and adverse human health outcomes.