Unequal pathways: Mobility, socioeconomic status, and the stratification of concurrent environmental exposures

Urban residents are simultaneously exposed to a complex mix of environmental factors, including risks like air pollution and noise, and benefits like green spaces. Previous research often neglects the dynamics of human mobility and co-exposures, relying on static, residence-based assessments. This study investigates how daily mobility shapes simultaneous exposures to fine particulate matter (PM₂.₅), noise, and green space, and how these relationships are stratified by socioeconomic status (SES). Using high-resolution GPS and mobile sensing data from 800 participants in Hong Kong, we analyzed the complex interactions among mobility, SES, and composite environmental exposures. Our findings reveal mobility is a double-edged sword: while increasing noise exposure, it can reduce PM₂.₅ and enhance green space exposure. Crucially, these consequences are not uniform, creating systematically differentiated environmental experiences among social groups. This supports the theory of “asymmetrical between-individual dispersion,” where exposures are not random but follow predictable, socially stratified patterns. For instance, long-distance mobility improves environmental quality for high-income and unemployed individuals but is associated with poorer outcomes for middle-income commuters and students from the same affluent neighborhoods. These results highlight the inadequacy of traditional approaches, demonstrating that neither focusing solely on residential environments nor simply promoting mobility can solve environmental inequity. Instead, effective policies must address the unique mobility constraints of different social groups. Our study provides critical insights for developing more targeted and equitable urban planning and public health interventions.