Effects of air pollution on emergency room visits for mental disorders: risks and effect modification by comorbid physical disorders and personal characteristics

Emerging evidence suggests that exposure to ambient air pollution negatively impacts mental health. However, little is known about potential moderators of such effects, including pre-existing physical disorders and personal characteristics. This study investigated if the effects of daily changes in levels of air pollutants among individuals with mental disorders (MDs) vary depending on comorbid physical disorders, age, sex, or race/ethnicity. We used a time-stratified case-crossover design that compared the levels of PM _2.5 and NO _2 on days leading up to MD-related emergency room (ER) visits to levels on control days. The sample consisted of individuals with MDs for their primary diagnosis, including both patients with a second diagnosis and those without. We conducted a stratified analysis to examine potential effect modifications by individuals’ demographic characteristics (sex, age, and race/ethnicity) or a diagnosis of a physical disorder (cardiovascular disease, diabetes mellitus, and respiratory disease). We found that both PM _2.5 and NO _2 were significantly associated with ER visits for MDs. Per 10 µ g m ^−3 increase in daily PM _2.5 and per 10 ppb increase in NO _2 concentration were associated with 1.07% (95% CI: 0.81%, 1.34%) and 0.56% (95% CI: 0.42%, 0.69%) increase in ER visits for MDs, respectively. We also found significantly greater susceptibility among younger persons (below 18 years old), Black, and individuals with respiratory disease. Exposures to both PM _2.5 and NO _2 were significantly associated with ER visits for MDs, and these adverse effects were more pronounced among youth, Black and individuals with respiratory disease as a comorbid physical disorder.