Allaouat S, Yli-Tuomi T, Tiittanen P, et al. - This study was undertaken to investigate the relationships of long-term exposure to PM _2.5 from road traffic and residential wood combustion with the prevalence of depression in the Helsinki region, Finland. Researchers performed a cross-sectional analysis based on the Helsinki Capital Region Environmental Health Survey including a total of 5,895 individuals between 2015 and 2016. No convincing evidence of an effect of long-term exposure to PM _2.5 from road traffic or residential wood combustion on depression was observed.