Defining "Overburdened Communities" in State Level Legislation Using Cumulative Impacts Frameworks to Inform Environmental Decision-Making: Implications for Environmental and Health Justice.

Problem Statement: Geographic-specific strategies for reducing air pollutants are of increasing interest for informing policies that reduce disparate air pollution exposure and health impacts. State legislation identifying such geographic areas use varying definitions, often focused on pollutant levels and/or population characteristics, with implications that are not well understood. Research Question: How do commonly used legislative definitions of overburdened communities (OBCs) differ in capturing areas that experience excess air pollutants? What are implications for eliminating excess pollutant exposure and health inequities? Methods: We extracted OBC definitions from state legislation using cumulative impact frameworks introduced or passed before May 2024. Using Michigan as a case study, we calculated correlations, sensitivity, and specificity of common OBC indicators and thresholds with PM2.5 concentration at the census block group (CBG) level. We used generalized linear mixed models to forecast change over time (2019-2039) in PM2.5 disparities using selected OBC definitions and various scenarios. Results: OBC definitions that included race/ethnicity had significantly larger disparities in PM2.5 concentration, compared with definitions that foregrounded income. Forecasting models indicate increasing inequalities over time for all OBC definitions using current and moderately accelerated intervention scenarios: Inequalities decline or disappear only under modeling scenarios which double or quadruple current rates of change. Conclusion: Differences in PM2.5 concentrations were largest when OBC definitions included race/ethnicity, and if current trends continue, are projected to increase over time, regardless of OBC definition. Exposure inequalities for OBCs defined using race and ethnicity are only eliminated under scenarios that double or quadruple current rates of reduction.