Exposure to fine particulate matter constituents and cognitive function performance, potential mediation by sleep quality: A multicenter study among Chinese adults aged 40–89 years

•PM2.5 components, particularly those from combustion-related sources, are associated with cognitive decline.•Sleep quality plays a mediation role in the association between PM2.5 and its chemical composition and cognitive decline.•Higher greenspace is associated with lower risk of cognitive decline associated with PM2.5 components.