A comparative study of methods for calculating the oxidative potential (OP) of atmospheric particulate matter

Abstract

The oxidative potential (OP) of particulate matter (PM) is a pivotal metric to evaluate the potential health effects of air pollution. However, the variety of assays and protocols available to measure the OP poses a challenge for comparing one study with another. The present study aims to provide an analysis comparing four calculation methods for determining the OP. These methods include the use of calibration curves (CURVE), absorbance values (ABS), and two concentration-based (CC1 and CC2) methods. Two acellular assays, dithiothreitol (DTT; OP^DTT) and ascorbic acid (AA; OP^AA), were chosen to be examined. The application of these assays led to varying OP results depending on the applied calculation method. Regarding results, first of all, there is a notable agreement between the ABS and CC2 methods across both the DTT and AA assays. Second, however, for both assays, the CC1 method consistently leads to higher OP values, with OP^DTT variations of up to 18% compared to ABS and CC2, and OP^AA variations of up to 12%. Third, the CURVE method yields OP^DTT and OP^AA values that are up to 10% and 19% higher than those calculated by the ABS and the CC2 methods, respectively. Therefore, both the ABS and CC2 methods are recommended for calculating OP values, as they have shown better consistency across different PM samples. These findings underscore the importance of defining standardizing OP protocols which should explicitly include all needed calculation steps in order to further develop the OP metric into a comparable measure linking air quality and human health.