TwinAIR health study: protocol for a European multi-centred, longitudinal study on indoor environmental quality (IEQ) related health and well-being

The term indoor environmental quality (IEQ) encompasses indoor air quality (IAQ), temperature, humidity, noise, and light. As people spend approximately 90% of their time indoors, at work, school, home, or during travel, understanding the relationship between IEQ and health is essential for health promotion, disease prevention, and sustainable building design and management. As part of the EU-funded TwinAIR project, the TwinAIR health study is a multi-centered, longitudinal investigation of how IEQ factors influence health and well-being across diverse European indoor spaces. This protocol describes a holistic study design integrating subjective and objective IEQ and health assessments and evaluating potential IEQ intervention effects. The TwinAIR health study will recruit and longitudinally follow 900 participants across 45 indoor spaces in five European countries (Germany, Greece, Spain, Sweden, and the United Kingdom), spanning work, study, leisure, and transport settings. Continuously measured IEQ parameters, including light, noise, temperature, humidity, nitrogen dioxide (NO2), ozone (O3), carbon dioxide (CO2), particulate matter (PM), particle number (PN), typical particle size (TPS), total volatile organic compounds (TVOC), and formaldehyde (HCHO), are assessed using advanced sensors with one-minute resolution. Sensor data are integrated with software-based digital twins and a data management platform. Health and well-being data include questionnaires assessing IEQ perceptions, respiratory and allergic symptoms, general health, mental health, somatization, well-being, and productivity, alongside objective measures including spirometry and skin and nasal samples for microbiome and resistome analyses. Air purification interventions are implemented in selected indoor spaces. The longitudinal design enables evaluation of intervention effects on IEQ and occupant health and well-being. The TwinAIR health study addresses the growing impact of indoor environments on health and well-being and aims to elucidate the interactions between IEQ parameters, occupant behaviours, building management practices, and health outcomes, an area that remains comparatively understudied relative to outdoor environmental research. The study will generate actionable insights for creating and managing healthier indoor spaces using innovative sensing technologies and comprehensive health assessments. Findings will inform evidence-based strategies to guide healthier indoor space design and management in Europe and beyond.