The HARMONIE project takes a holistic approach to support informed policy- making by improving AP and noise monitoring, modeling, and forecasting as well as by providing tools to assess the health impact of actions on VP and the impact of actions in the long run on economy and sustainability of policies. The consortium will work in pilot cities to: 1) Enhance environmental monitoring and modelling by identifying key harmful variables. 2) Assess citizen exposure based on urban demographics, mobility, and vulnerability factors. 3) Evaluate health effects, both at the individual level (based on Digital Twin Lungs) and at the population level (computing mortality and morbidity). These components will be tested in real-world city scenarios, prioritizing pollution-abatement strategies. The methodology includes two key approaches: ● PILOTS: Data collection from Gävle (GAV), Sarajevo (SRJ), Lausanne (LAU), Barcelona (BCN) city and province, and Barakaldo (BRK), identifying vulnerable populations, monitoring pollutants (AQ & noise), and analyzing related health outcomes. ● DIGITAL TWIN: A Citizen-Centric Digital Twin (CCDT) will visualize pollution hotspots, engage citizens through interactive platforms, and integrate a social dynamics model to assess both health and healthcare system impacts under different scenarios. HARMONIE will enable ‘What-If’ scenario simulations within the CCDT, allowing policymakers to benchmark strategies and select optimal interventions. To ensure long-term impact, the project will integrate developments into existing city infrastructures, enhancing policy communication and decision-making with cutting-edge digital tools. By integrating community-driven data, What-If scenarios, and behavioral insights, it helps overcome psychological and social barriers to zero-pollution initiatives. Through dynamic simulations and feedback mechanisms, it engages citizens and institutions to develop actionable strategies tailored to urban communities.