Environmental Exposure and Mental Health in Hong Kong: Protocol for a GPS- and Biosensor-Based Observational Study.

BACKGROUND: Environmental exposure, including green-blue space and walkability, may influence mental health through various physiological pathways. Traditional methods have limitations in capturing dynamic environmental exposure effects on mental health. OBJECTIVE: This study aims to investigate the associations between minute-level environmental exposure and stress-related biomarkers using GPS-based measurements and wrist-worn biosensors in an urban population. METHODS: In this prospective observational study, we will recruit 750 participants (aged 18-80 years) in Hong Kong from September 2024 to December 2026. This includes a pilot study supported by internal funds starting in September 2024 and external funding from the Health and Medical Research Fund by the Hong Kong Health Bureau in July 2025. Participants will undergo a 1-week experiment wearing biosensors and carrying GPS devices while completing daily surveys and entry and exit questionnaires. Primary outcomes include digital biomarkers (electrodermal activity, blood volume pulse, and skin temperature) from wrist-worn sensors and associations with the environmental exposures of air pollution, urban density, and green-blue space access. Secondary outcomes comprise questionnaire responses, physical activity metrics from accelerometer data, and environmental exposure assessments, including mobility barriers, land use mix, road accessibility, and thermal conditions. Focus groups will be conducted to refine study protocol and assess device-wearing experience. RESULTS: The study received ethical approval from the Human Ethic Research Committee (award numbers: EA240125 and EA240514). As of June 30, 2025, a total of 150 participants completed the pilot study (September 2024 onwards), achieving a 94% (141/150) completion rate with strong device compliance (141/150, 94% valid biosensor days; 137/150, 91% daily questionnaires). Protocol refinements based on participant feedback were implemented without altering core instruments. The main study supported by the Health and Medical Research Fund, commenced in July 2025, with 30 participants enrolled as of September 2025. Data collection for 750 participants will continue until December 2026. We are at an early stage of data cleaning and preprocessing for the pilot study. Data analysis is expected to be completed by June 2027, with results anticipated to be published in 2027 and 2028. CONCLUSIONS: This study's innovative integration of continuous environmental monitoring and stress-related biomarker may provide new insights into environment-health relationships. Findings will inform public health initiatives for mental well-being promotion and urban planning interventions. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/84919.