Objective To evaluate the effects of ambient air pollution on rheumatoid arthritis (RA) incidence in a racially/ethnically diverse population. Methods This analysis included 42,152 California Multiethnic Cohort (MEC) participants, ages 65 or older (>70% African American and Latino adults) who were enrolled in the Fee‐for‐Service component of Medicare (2001‐2018). We employed multivariable Cox proportional hazards regression to examine the associations of time‐varying air pollutants based on spatiotemporal models with RA incidence (n=2,027) after adjusting for demographics, neighborhood socioeconomic status (nSES), smoking, work and other exposures. Results RA incidence increased with exposure to fine particulate matter (PM) with diameter ≤2.5 μm (PM 2.5 ) (hazard ratios (HR) [95% CI] per 2 μg/m 3 =1.20 [1.16‐1.23]) and nitrogen dioxide (NO 2 ) HR per 10 μg/m 3 =1.44 [1.35‐1.52]). Air pollutant levels and risk associations were higher in African American and Latino than in Japanese American and White adults (P heterogeneity <0.05). The RA‐PM 2.5 association was higher in men (1.23 [1.15‐1.32]) than in women (1.17 [1.12‐1.21] P heterogeneity =0.06). RA associations with PM 2.5 (and NO 2 ) did not differ by demographics, smoking, or other lifestyle factors but the HR associated with PM 2.5 was higher among those with high‐risk work (longest occupation in labor/craftsman work and exposed to ≥10 years in one or more of 13 industries) (1.29[1.18‐1.41]) than those without high‐risk work exposures (1.16 [1.12‐1.21] P heterogeneity =0.04). Conclusion Exposure to PM and gaseous pollution associates with increased RA incidence after age 65, particularly among African American and Latino adults. Further characterization of air pollution's contribution to racial and ethnic disparities in RA risk is warranted.

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