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[Display omitted] Our understanding of the impact of long-term exposures to PM 2.5 constituents and sources on mortality is limited. To examine associations between long-term exposures to PM 2.5 constituents and sources and cause-specific mortality in US older adults. We obtained demographic and mortality data for 15.4 million Medicare beneficiaries living within the conterminous United States (US) between 2000 and 2008. We assessed PM 2.5 constituents exposures for each beneficiary and used factor analysis and residual-based methods to characterize PM 2.5 sources and mixtures, respectively. In age-, sex-, race- and site- stratified Cox proportional hazard models adjusted for neighborhood socio-economic status (SES), we assessed associations of individual PM 2.5 constituents, sources, and mixtures and cause-specific mortality and examined modification of these associations by participant demographics and location of residence. We assessed the robustness of our findings to additional adjustment for behavioral risk factors and to alternate exposure definitions and exposure windows. Hazard ratios (HR) were highest for all causes of death, except COPD, for PM 2.5 constituents and the coal combustion-related PM 2.5 components, with no evidence of confounding by behavioral covariates. We further found Pb and metal-related PM 2.5 components to be significantly associated with increased HR of all causes of death, except COPD and lung cancer mortality, and nitrate (NO 3 –) and silicon (Si) and associated source-related PM 2.5 components (traffic and soil, respectively) to be significantly associated with increased all-cause, CVD, respiratory and all cancer-related mortality HR. Associations for other examined constituents and mortality were inconsistent or largely null. Our analyses of mixtures were generally consistent with these findings. Mortality HRs were greatest for minority, especially Black, low-income urban, younger, and male beneficiaries. PM 2.5 components related to coal combustion, traffic, and to a lesser extent, soil were strongly associated with mortality from CVD, respiratory disease, and cancer. [ABSTRACT FROM AUTHOR]