The use of race and ethnicity in air pollution epidemiology and methodological recommendations: A scoping review focusing on California

Air pollution remains a significant global health risk, and exposure to air pollutants can lead to multiple health issues across the life course. Air pollution is also an environmental justice issue and plays a crucial role in health disparities across racial and ethnic groups, through both differential exposure and differential vulnerability. Historical patterns of discriminatory siting of emission sources have led to differential exposure to air pollution among racial and ethnic groups. Differential vulnerability, influenced by social factors and community composition, further exacerbates health inequities. Given these complex mechanisms through which race and ethnicity (RE) influence both exposure and vulnerability to air pollution, it is important to understand how RE is operationalized in air pollution epidemiology and identify methodological opportunities. We conducted a scoping review to summarize the use of RE in air pollution epidemiology literature with a focus on California. From January 2000 to July 2025, we identified a total of 178 publications, excluding those that only used RE as a confounder. The number of studies exploring air pollution disparity across RE or RE as effect modifiers for the air pollution-outcome relationship increased over time, but the number of publications exploring the mediating role of air pollution in outcome disparity across RE remained low. We identified several methodological practices that warrant further consideration and provided corresponding methodological recommendations that can help researchers and policymakers better understand current practices for consideration of RE in air pollution-related health studies.