Air pollution and suicide mortality in the UK: implications for environmental and mental health policy.

Air pollution is a well-established risk factor for physical illness and premature mortality, yet its relationship with suicide remains less well understood, particularly at the national level and over longer periods of exposure. Although previous studies have reported positive associations between particulate matter and suicide, evidence remains heterogeneous, and national longitudinal analyses are limited. This study examines the association between fine particulate matter (PM₂.₅) concentrations and suicide mortality across local authorities in the UK between 2015 and 2023. Suicide data obtained from the UK Office for National Statistics were combined with modelled PM₂.₅ estimates from the Department for Environment, Food and Rural Affairs, resulting in a balanced panel of more than 2200 local authority-year observations. Fixed-effects panel regression models were employed to account for unobserved time-invariant local characteristics and common year-specific shocks, while nonlinear specifications were estimated to examine potential threshold effects. The descriptive analysis revealed a negative cross-sectional association between PM₂.₅ concentrations and suicide rates. However, after controlling for local authority and year fixed effects, PM₂.₅ was positively and significantly associated with suicide mortality (β = 0.221, p = 0.007). The nonlinear model further identified a statistically significant U-shaped relationship, with an estimated turning point at approximately 7.8 µg/m