Interactions between Ambient Air Particles and Greenness on Cause-specific Mortality in Seven Korean Metropolitan Cities, 2008–2016

This study aims to investigate the association of particulate matter with an aerodynamic diameter smaller than 10 μm (PM(10)) and greenness with cause-specific mortality and their interactions in seven Korean metropolitan cities. We obtained the annual standardized cause-specific mortality rates, annual mean concentration of PM(10), and annual Normalized Difference Vegetation Index (NDVI) for 73 districts for the period 2008–2016. We used negative binomial regression with city-specific random effects to estimate the association of PM(10) and greenness with mortality. The models were adjusted for potential confounders and spatial autocorrelation. We also conducted stratified analyses to investigate whether the association between PM(10) and mortality differs by the level of greenness. Our findings suggest an increased risk of all causes examined, except respiratory disease mortality, with high levels of PM(10) and decreased risk of cardiovascular-related mortality with a high level of greenness. In the stratified analyses, we found interactions between PM(10) and greenness, but these interactions in the opposite direction depend on the cause of death. The effects of PM(10) on cardiovascular-related mortality were attenuated in greener areas, whereas the effects of PM(10) on non-accidental mortality were attenuated in less green areas. Further studies are needed to explore the underlying mechanisms.