Ambient air pollution exposure and years of life lost due to suicide: synergistic effect with high temperature

Suicide is a major cause of death globally, with recent research highlighting environmental factors. However, studies often focus on individual impacts of air pollutants and temperature, neglecting their synergistic effects. This study assessed the impact of air pollutant exposure combined with temperatures on suicide, using years of life lost (YLLs) as a measure of premature mortality. A generalized additive model examined short-term links between air pollutants including particles < 2.5 μm (PM_2.5) and < 10 μm (PM₁₀), ozone (O₃), sulfur dioxide (SO₂), nitrogen dioxide (NO₂), and carbon monoxide (CO) exposures and YLLs due to suicide in Seoul, South Korea, between 2002 and 2019, considering lag effects within 7 days. Synergistic effects of air pollutants and temperature were evaluated using a dummy variable, stratifying temperature levels into low and high (> 90th percentile). During the study period, there were 43,642 suicides, with an average daily YLLs of 193 years. Among the pollutants, NO₂ and O₃ showed significant associations with YLLs due to suicide. An interquartile range increase of 17.8 ppb for NO₂ and 22.1 ppb for O₃ was associated with increases in YLLs due to suicide by 4.08 and 5.72 years, respectively. All air pollutants and high temperatures were found to have significant synergistic effects on YLLs due to suicide (PM₁₀ [11.83 years; P_interact = 0.01]; PM_2.5 [10.74 years; P_interact = 0.01]; NO₂ [14.52 years; P_interact = 0.01]; SO₂ [8.72 years; P_interact = 0.04]; O₃ [10.02 years; P_interact = 0.08]; and CO [11.42 years; P_interact = 0.03]). The results support creating suicide prevention policies to reduce premature deaths.