High temperatures are associated with adverse respiratory health outcomes and increases in ambient air pollution. Limited research has quantified air pollution's mediating role in the relationship between temperature and respiratory morbidity, such as emergency department (ED) visits. In this study, we conducted a causal mediation analysis to decompose the total effect of daily temperature on respiratory ED visits in Los Angeles from 2005 to 2016. We focused on ambient ozone as a mediator because its precursors and formation are directly driven by sunlight and temperature. We estimated natural direct, indirect, and total effects on the relative risk scale across deciles of temperature exposure compared to the median. We utilized Bayesian additive regression trees (BART) to flexibly characterize the nonlinear relationship between temperature and ozone and quantified uncertainty via posterior prediction and the Bayesian bootstrap. Our results showed that ozone partially mediated the association between high temperatures and respiratory ED visits, particularly at moderately high temperatures. We also validated our modeling approach through simulation studies. This study extends the existing literature by considering acute respiratory morbidity and employing a flexible modeling approach, offering new insights into the mechanisms underlying temperature-related health risks.

翻译：高温与不良呼吸健康结局及环境空气污染加剧相关。现有研究鲜有量化空气污染在气温与呼吸系统发病率（如急诊就诊）关系中的中介作用。本研究采用因果中介分析方法，分解了2005年至2016年洛杉矶地区日气温对呼吸系统急诊就诊的总效应。我们聚焦环境臭氧作为中介变量，因其前体物生成与形成过程直接受日照和温度驱动。通过对比中位数气温暴露，我们估算了十分位温度区间内的自然直接效应、间接效应及总效应的相对风险比。研究采用贝叶斯加性回归树（BART）灵活刻画气温与臭氧的非线性关系，并通过后验预测与贝叶斯自助法量化不确定性。结果表明，臭氧部分中介了高温与呼吸系统急诊就诊的关联，在中等偏高温度区间尤为显著。我们通过模拟研究验证了建模方法的可靠性。本研究通过关注急性呼吸系统发病率并采用灵活建模方法，拓展了现有文献体系，为揭示温度相关健康风险的内在机制提供了新见解。