Oxidative potential of particulate matter collected at sites with different source characteristics

The oxidative potential (OP) of particulate matter (PM) has been proposed as a more health relevant metric than PM mass. Different assays exist for measuring OP and little is known about how the different assays compare. To assess the OP of PM collected at different site types and to evaluate differences between locations, size fractions and correlation with PM mass and PM composition for different measurement methods for OP. PM2.5 and PM10 was sampled at 5 sites: an underground station, a farm, 2 traffic sites and an urban background site. Three a-cellular assays; dithiothreitol (OPDTT), electron spin resonance (OPESR) and ascorbate depletion (OPAA) were used to characterize the OP of PM. The highest OP was observed at the underground, where OP of PM10 was 30 (OPDTT) to >600 (OPESR) times higher compared to the urban background when expressed as OP/m3 and 2–40 times when expressed as OP/μg. For the outdoor sites, samples from the farm showed significantly lower OPESR and OPAA, whereas samples from the continuous traffic site showed the highest OP for all assays. Contrasts in OP between sites were generally larger than for PM mass and were lower for OPDTT compared to OPESR and OPAA. Furthermore, OPDTT/μg was significantly higher in PM2.5 compared to PM10, whereas the reverse was the case for OPESR. OPESR and OPAA were highly correlated with traffic-related PM components (i.e. EC, Fe, Cu, PAHs), whereas OPDTT showed the highest correlation with PM mass and OC. Contrasts in OP between sites, differences in size fractions and correlation with PM composition depended on the specific OP assay used, with OPESR and OPAA showing the most similar results. This suggests that either OPESR or OPAA and OPDTT can complement each other in providing information regarding the oxidative properties of PM, which can subsequently be used to study its health effects. •The oxidative potential (OP) of PM was highly elevated at an underground station.•Outdoors, PM along a highway with continuous traffic showed the highest activity.•Contrasts in OP between sites depended on the specific OP assay used.•The OP methods studied also differed in respect to correlation with PM composition.•Different OP assays can provide complementary data about the oxidative properties of PM.