Background: The aim of this study was to investigate the associations between ambient air pollution and emergency department (ED) visits for depression.

Methods: Health data were retrieved from the National Ambulatory Care Reporting System. ED visits for depression were retrieved from the National Ambulatory Care Reporting System using the International Classification of Diseases (ICD-10), Tenth revision codes; ICD-10: F32 (mild depressive episode) and ICD-10: F33 (recurrent depressive disorder). A case-crossover design was employed for this study. Conditional logistic regression models were used to estimate odds ratios.

Results: For females, exposure to ozone was associated with increased risk of an ED visit for depression between 1 and 7 days after exposure, for males, between 1 and 5, and 8 days after exposure, with odds ratios ranging between 1.02 and 1.03.

Conclusions: These findings suggest that, as hypothesized, there is a positive association between exposure to air pollution and ED visits for depression.