Indoor–Outdoor Air Quality Interactions in University Classrooms: Exposure, Perception, and Health Implications

Indoor air quality (IAQ) is a critical determinant of human health, particularly in environments where occupants spend prolonged periods of time, such as higher education classrooms. These spaces are characterised by high occupancy densities, frequent indoor activities, and continuous exchange of air with the outdoor environment through ventilation systems, window opening, and building leakage. As a result, indoor air quality in university buildings reflects a complex interaction between indoor emission sources, outdoor air pollution, occupant behaviour, and indoor–outdoor transport processes.

Classroom environments are influenced by multiple indoor sources, including occupant-related emissions, resuspension of particulate matter due to movement, cleaning activities, and emissions from building materials and furnishings. Also, outdoor-origin pollutants such as fine particulate matter and gaseous contaminants infiltrate indoor spaces, with their impact depending on ventilation strategies, building envelope characteristics, and user behaviour. Once indoors, pollutants may undergo physical and chemical transformations, further modifying exposure profiles and contributing to cumulative health burdens.

This study investigates indoor air quality in higher education classrooms using an integrated approach that combines field measurements with occupant perception and health-related information. Environmental monitoring focuses on key parameters relevant to indoor–outdoor pollutant exchange, including carbon dioxide as a proxy for ventilation adequacy, particulate matter concentrations, air temperature, and relative humidity. Objective measurements are complemented by surveys assessing perceived air quality, comfort, ventilation, and the presence or aggravation of existing health conditions. This combined methodology enables the evaluation of both exposure conditions and the human factors that influence pollutant dynamics.

Results indicate that elevated indoor pollutant levels often arise from the combined influence of indoor emissions and outdoor infiltration, particularly in naturally ventilated classrooms located in urban environments. Occupant behaviour, such as window opening practices and classroom occupancy patterns, plays a decisive role in shaping indoor pollutant concentrations and perceived air quality. Perceptions of stale or polluted air frequently coincide with conditions of inadequate ventilation or increased outdoor pollution ingress, underscoring the importance of behavioural and building-related factors in exposure assessment.

The findings highlight that perceptions of indoor air quality act as valuable indicators of the cumulative effects of multiple environmental stressors and can provide signals of exposure-related health risks, especially for individuals with pre-existing respiratory conditions. The interconnected nature of indoor and outdoor air quality, where interventions targeting ventilation, building operation, or user behaviour may simultaneously influence indoor exposures and outdoor emissions.

Understanding indoor air quality in higher education institutions requires a holistic perspective that integrates indoor emission sources, indoor–outdoor transport processes, occupant behaviour, and health outcomes. This approach contributes to advancing knowledge of the indoor–outdoor air pollution interface and supports the development of effective interventions and evidence-based policies aimed at improving air quality and protecting human health.

 

Keywords: Indoor Air Quality; Higher Education; Environmental Perception; Health and Well-being; Classroom environments

Acknowledgements: This work is supported by National Funds by FCT – Portuguese Foundation for Science and Technology, under the projects UID/04033/2025: Centre for the Research and Technology of Agro-Environmental and Biological Sciences (https://doi.org/10.54499/UID/04033/2025) and LA/P/0126/2020 (https://doi.org/10.54499/LA/P/0126/2020).

This research was supported by the European Union under the Breath IN Erasmus+ project 2023-1-PT01-KA220_HED-00153118.