Source-Specific PM_2.5 Exposure and Atrial Fibrillation Risk in U.S. Older Adults: A Nationwide Cohort Study

Fine particulate matter (PM_2.5) is associated with an increased risk of atrial fibrillation (AF), but the effects of individual PM_2.5 sources remain unclear. We evaluated the relationship between long-term exposure to source-specific PM_2.5 and incident AF among 26.3 million U.S. Medicare beneficiaries from 2000 to 2019. We resolved PM_2.5 sources using the Multilinear Engine model based on PM_2.5 components data from monitoring stations. Annual ZIP code-level exposures were assigned using inverse-distance weighting of monitoring stations within a 100 km buffer. Cox proportional hazards models were used to estimate AF risk per interquartile range (IQR) increase in source-specific PM_2.5 concentrations, adjusting for demographic and socioeconomic factors and other environmental covariates. Over 171.6 million person-years of follow-up, 4.44 million incident AF cases were identified. Exposure to PM_2.5 from vehicle emissions (HR 1.029, 95% CI 1.028-1.030), heavy oil and coal combustion (HR 1.048, 95% CI 1.046-1.050), secondary sulfate (HR 1.056, 95% CI 1.053-1.058), and secondary nitrate (HR 1.032, 95% CI 1.030-1.034) was significantly associated with higher AF risk. In contrast, biomass burning and soil and dust exhibited only modest associations, and secondary organic aerosols (SOA) showed no overall effect. Regional analyses revealed geographic heterogeneity: fossil-fuel-related sources drove AF risk in most regions, secondary sulfate and nitrate had the strongest effects in the southern U.S., and SOA was more strongly associated with AF in the West. These findings highlight the differential toxicity and regional heterogeneity of PM_2.5 sources in AF risk and emphasize the need for targeted, region-specific air quality regulations focusing on traffic and industrial emissions to mitigate AF incidence in older adults.