Short‐Term Exposure to Ambient Ozone and Fine Particulate Matter and Its Components Increases the Risk of In‐Hospital Adverse Outcomes in Patients With Acute Myocardial Infarction: A Time‐Stratified Case‐Crossover Study

Background Although exposure to ozone (O 3 ) and fine particulate matter with a diameter of ≤2.5 μm (PM 2.5 ) has been associated with increased cardiovascular events and hospitalizations, their association with in‐hospital outcomes among patients with acute myocardial infarction remains uncertain. Methods A time‐stratified case‐crossover study was conducted using patients with acute myocardial infarction admitted to hospitals in Beijing from 2013 to 2019. Daily levels of O 3 and PM 2.5 and its components (sulfate, nitrate, ammonium, organic matter, and black carbon) were assessed. Conditional logistic regression estimated exposure–response relationships between pollutants and in‐hospital death. The relative excess risk due to interaction was used to quantify interactions between O 3 and each PM 2.5 component. Results O 3 exhibited a threshold effect: When the concentration on the admission day exceeded 90 μg/m 3 , in‐hospital mortality risk increased significantly. PM 2.5 and each component showed linear exposure–response relationships. At a 2‐day moving average, each 10 μg/m 3 increase in PM 2.5 was associated with a 1.4% (95% CI, 0.9%–1.9%) increase in in‐hospital death. Significant positive multiplicative interactions were observed between O 3 and all PM 2.5 components, with notable synergistic effects for O 3 –organic matter (relative excess risk due to interaction, 0.155 [95% CI, 0.053–0.258]) and O 3 –black carbon (relative excess risk due to interaction, 0.137 [95% CI, 0.033–0.240]). The effects of O 3 were stronger in summer, while the effects of PM 2.5 components were more pronounced in winter. Joint exposure resulted in a higher mortality burden than single‐pollutant exposure. Conclusions Short‐term exposure to O 3 and PM 2.5 components increases in‐hospital mortality risk in patients with acute myocardial infarction, with synergistic effects between ozone and organic matter or O 3 and black carbon.