Associations between Ambient Fine Particulate Oxidative Potential and Cardiorespiratory Emergency Department Visits

BACKGROUND: Oxidative potential (OP) has been proposed as a measure of toxicity of ambient particulate matter (PM). OBJECTIVES: Our goal was to address an important research gap by using daily OP measurements to conduct population-level analysis of the health effects of measured ambient OP. METHODS: A semi-automated dithiothreitol (DTT) analytical system was used to measure daily average OP ([Formula: see text]) in water-soluble fine PM at a central monitor site in Atlanta, Georgia, over eight sampling periods (a total of 196 d) during June 2012–April 2013. Data on emergency department (ED) visits for selected cardiorespiratory outcomes were obtained for the five-county Atlanta metropolitan area. Poisson log-linear regression models controlling for temporal confounders were used to conduct time-series analyses of the relationship between daily counts of ED visits and either the 3-d moving average (lag 0–2) of [Formula: see text] or same-day [Formula: see text]. Bipollutant regression models were run to estimate the health associations of [Formula: see text] while controlling for other pollutants. RESULTS: [Formula: see text] was measured for 196 d ([Formula: see text] , [Formula: see text]). Lag 0–2 [Formula: see text] was associated with ED visits for respiratory disease ([Formula: see text] , 95% confidence interval (CI): 1.00, 1.05 per interquartile range increase in [Formula: see text]), asthma ([Formula: see text] , 95% CI: 1.03, 1.22), and ischemic heart disease ([Formula: see text] , 95% CI: 1.03, 1.38). Same-day [Formula: see text] was not associated with ED visits for any outcome. Lag 0–2 [Formula: see text] remained a significant predictor of asthma and ischemic heart disease in most bipollutant models. CONCLUSIONS: Lag 0–2 [Formula: see text] was associated with ED visits for multiple cardiorespiratory outcomes, providing support for the utility of [Formula: see text] as a measure of fine particle toxicity. https://doi.org/10.1289/EHP1545