The primary objective of EPIC-AIR is to evaluate the feasibility and potential effectiveness of integrating real-time air pollution monitoring into CR and PR programmes via an online platform that delivers both exercise prescription and air pollution guidance. Specific objectives are: (1) to determine whether access to real-time air quality data reduces personal pollution exposure (PM2.5, PM10, NO2) during outdoor physical activity in CR/PR patients and healthy volunteers; (2) to evaluate the usability and acceptability of the platform in a clinical rehabilitation context; (3) to assess the feasibility of the trial design, including recruitment, randomisation, retention, and adherence rates; (4) to measure the impact of the intervention on physical activity levels, health-related quality of life, and cardiovascular biomarkers; and (5) to inform the design and sample size of a future definitive randomised controlled trial.