PM2.5 air pollution components and mortality in Denmark

Background: Ambient fine particulate matter (PM2.5) causes millions of deaths every year worldwide. Identification of the most harmful types of PM2.5 would facilitate efficient prevention strategies. Objectives: The aim of this study was to investigate associations between components of PM2.5 and mortality in a nation-wide Danish population. Methods: Our study base was Danes born 1921-1985 and aged 30-85 years, who were followed up for mortality from 1991 to 2015. We included 678,465 natural cause mortality cases and selected five age, sex and calendar time matched controls to each case from the study base. We retrieved the address history of the study population from Danish registries and assessed five-year average concentrations of eight PM2.5 components using deterministic Chemistry-Transport Models air pollution models. We estimated mortality rate ratios (MRRs) by conditional logistic regression and adjusted for socio-demographical factors at individual and neighborhood level. Results: Single pollutant models showed the strongest associations between natural cause mortality and an interquartile increase in sulfate particles (SO4--) (MRR: 1.123; 95 % CI: 1.100-1.147 per 1.5 mu g/m(3)) and secondary organic aerosol (SOA) (MRR: 1.054; 95 % CI: 1.048-1.061 per 0.050 mu g/m(3)). Two-pollutant models showed robust associations between SO4-- and SOA and natural cause mortality. Elemental carbon and mineral dust showed robust associations with higher respiratory and lung cancer mortality. Conclusion: This nation-wide study found robust associations between natural cause mortality and SO4-- particles and SOA, which is in line with the results of previous studies. Elemental carbon and mineral dust showed robust associations with higher respiratory and lung cancer mortality.