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Abstract Most fine ambient particulate matter (PM_2.5)-based epidemiological models use globalized concentration-response (CR) functions assuming that the toxicity of PM_2.5is solely mass-dependent without considering its chemical composition. Although oxidative potential (OP) has emerged as an alternate metric of PM_2.5toxicity, the association between PM_2.5mass and OP on a large spatial extent has not been investigated. In this study, we evaluate this relationship using 385 PM_2.5samples collected from 14 different sites across 4 different continents and using 5 different OP (and cytotoxicity) endpoints. Our results show that the relationship between PM_2.5mass vs. OP (and cytotoxicity) is largely non-linear due to significant differences in the intrinsic toxicity, resulting from a spatially heterogeneous chemical composition of PM_2.5. These results emphasize the need to develop localized CR functions incorporating other measures of PM_2.5properties (e.g., OP) to better predict the PM_2.5-attributed health burdens. 

Abstract. Several automated instruments exist to measure the acellularoxidative potential (OP) of ambient particulate matter (PM). However,cellular OP of the ambient PM is still measured manually, which severelylimits the comparison between two types of assays. Cellular assays couldprovide a more comprehensive assessment of the PM-induced oxidative stress,as they incorporate more biological processes involved in the PM-catalyzedreactive oxygen species (ROS) generation. Considering this need, wedeveloped a semi-automated instrument, the first of its kind, for measuring thecellular OP based on a macrophage ROS assay using rat alveolar macrophages.The instrument named SCOPE – semi-automated instrument for cellularoxidative potential evaluation – uses dichlorofluorescein diacetate (DCFH-DA)as a probe to detect the OP of PM samples extracted in water. SCOPE iscapable of analyzing a batch of six samples (including one negative and onepositive control) in 5 h and is equipped to operate continuously for24 h with minimal manual intervention after every batch of analysis,i.e., after every 5 h. SCOPE has a high analytical precision asassessed from both positive controls and ambient PM samples (coefficient of variation (CoV)<17 %). The results obtained from the instrument were in good agreementwith manual measurements using tert-butyl hydroperoxide (t-BOOH) as thepositive control (slope =0.83 for automated vs. manual, R2=0.99)and ambient samples (slope =0.83, R2=0.71). We furtherdemonstrated the ability of SCOPE to analyze a large number of both ambientand laboratory samples and developed a dataset on the intrinsic cellular OPof several compounds, such as metals, quinones, polycyclic aromatichydrocarbons (PAHs) and inorganic salts, commonly known to be present inambient PM. This dataset is potentially useful in future studies toapportion the contribution of key chemical species in the overall cellularOP of ambient PM.