Optimization and Application of Analytical Assays for the Determination of Oxidative Potential of Outdoor and Indoor Particulate Matter

Abstract

Recent studies indicate that mass concentration alone is not the best parameter to assess the toxicity and the health effects of particulate matter (PM). Indeed, the chemical composition of the particles plays an important role, and oxidative potential (OP) measurements are being proposed as an alternative way to assess toxicity. The European Union (EU) is currently proposing a draft of the new air quality directive which includes OP measurements but does not specify the methods and/or protocols of analysis. In this light, the purpose of this study was to evaluate the feasibility of two literature assays, namely ascorbic acid (AA) and dithiothreitol (DTT), for routine PM analysis by testing urban PM filters from a one-year sampling campaign conducted by ARPA Lombardia. Indoor PM samples were also tested to emphasize the importance of monitoring closed spaces in which people spend most of their time. Following the optimization of the DTT assay, both methods proved to be suitable for large-scale PM analysis. The results show that the oxidative strength of urban PM is constant throughout the year for the outdoor samples (OPAA: 0.067–0.39 nmol min−1 m−3; OPDTT: 0.033–0.109 nmol min−1 m−3), indicating the need for routine OP monitoring. Instead, indoor areas were characterized by particles with a lower oxidative capacity (OPAA: 5.40–24 pmol min−1 m−3; OPDTT: 9.7–32 pmol min−1 m−3), driven both by lower concentrations and a different chemical composition. All the data collected highlight the need to add this parameter as part of the chemical characterization of PM, moving in the same direction as the new EU air quality directive.