Importance of ventilation and/or air cleaning in relation to risk of indoor transmission of infectious diseases: Insights from Prof. Lidia Morawska
05 February 2025
In a recent interview in February 2025, Professor Lidia Morawska shared her knowledge and experiences about indoor air quality and disease transmission, offering a view of current understanding and future directions in the field. The interview discussions are summarized below:
Key Transmission Factors
Professor Morawska outlined three essential elements for respiratory disease transmission: an infected person present in the space, susceptible individuals sharing that space, and conditions allowing pathogen accumulation. She emphasized that both the concentration of pathogens and exposure time are key factors in transmission risk.
Professor Morawska outlined three essential elements for respiratory disease transmission: an infected person present in the space, susceptible individuals sharing that space, and conditions allowing pathogen accumulation. She emphasized that both the concentration of pathogens and exposure time are key factors in transmission risk.
Shifting Understanding of Transmission Routes
Professor Morawska highlighted how public health authorities’ understanding of COVID-19 transmission evolved globally from an initial focus on surface contamination to recognition of airborne transmission as the primary route, drawing on scientific knowledge from recent decades. Professor Morawska clarified the misconception about infectious respiratory particle sizes, explaining that the traditional medical distinction between aerosols (below 5 micrometres) and droplets (above 5 micrometres ) has been abolished, as all respiratory particles larger than about 100 micrometres can be airborne and contribute to infection transmission.
Professor Morawska highlighted how public health authorities’ understanding of COVID-19 transmission evolved globally from an initial focus on surface contamination to recognition of airborne transmission as the primary route, drawing on scientific knowledge from recent decades. Professor Morawska clarified the misconception about infectious respiratory particle sizes, explaining that the traditional medical distinction between aerosols (below 5 micrometres) and droplets (above 5 micrometres ) has been abolished, as all respiratory particles larger than about 100 micrometres can be airborne and contribute to infection transmission.
Environmental Factors
The professor detailed how environmental conditions affect respiratory droplets. When expelled, water-based particles quickly shrink to 20-40% of their original size due to evaporation. Interestingly, recent research has shown that CO2 levels as low as 700-800 ppm can increase SARS-CoV-2 virus stability through increased acidity of respiratory particles containing the virus.
The professor detailed how environmental conditions affect respiratory droplets. When expelled, water-based particles quickly shrink to 20-40% of their original size due to evaporation. Interestingly, recent research has shown that CO2 levels as low as 700-800 ppm can increase SARS-CoV-2 virus stability through increased acidity of respiratory particles containing the virus.
Ventilation vs. Air Cleaning
While air-cleaning technologies can be helpful, Professor Morawska emphasized that proper ventilation should be the primary focus. Ventilation should be the main priority, ensuring a steady supply of fresh air. In naturally ventilated spaces, e.g. classrooms, open windows can often provide sufficient airflow, but concerns about temperature, noise, or safety often lead to their closure. When adequate ventilation isn't possible, air purifiers can help. However, they are not an ideal solution. To effectively reduce infection risks, broader air quality considerations must also be addressed. She discussed challenges with air purifiers in schools, noting that issues like noise often result in their underuse. She advocated for improving air purifiers by equipping them with low-pressure, low-noise filters and designing them to operate autonomously when pollutant concentrations exceed set limits.
Ongoing Efforts & Future Preparedness
Rather than focusing solely on future pandemics, Professor Morawska stressed the need to tackle existing respiratory diseases and epidemics they cause and minimizing infection risks from currently known pathogens. She recommended a layered approach combining proper ventilation, appropriate use of masks in high-risk situations, and awareness of indoor air quality.
While air-cleaning technologies can be helpful, Professor Morawska emphasized that proper ventilation should be the primary focus. Ventilation should be the main priority, ensuring a steady supply of fresh air. In naturally ventilated spaces, e.g. classrooms, open windows can often provide sufficient airflow, but concerns about temperature, noise, or safety often lead to their closure. When adequate ventilation isn't possible, air purifiers can help. However, they are not an ideal solution. To effectively reduce infection risks, broader air quality considerations must also be addressed. She discussed challenges with air purifiers in schools, noting that issues like noise often result in their underuse. She advocated for improving air purifiers by equipping them with low-pressure, low-noise filters and designing them to operate autonomously when pollutant concentrations exceed set limits.
Ongoing Efforts & Future Preparedness
Rather than focusing solely on future pandemics, Professor Morawska stressed the need to tackle existing respiratory diseases and epidemics they cause and minimizing infection risks from currently known pathogens. She recommended a layered approach combining proper ventilation, appropriate use of masks in high-risk situations, and awareness of indoor air quality.
Personal Protection Strategies
To monitor air quality and reduce personal risk, the professor carries a CO2 meter and N95 masks. She emphasized that while individual responsibility is important, building operators should ultimately be responsible for maintaining good indoor air quality.
To monitor air quality and reduce personal risk, the professor carries a CO2 meter and N95 masks. She emphasized that while individual responsibility is important, building operators should ultimately be responsible for maintaining good indoor air quality.
This interview highlights the complexity of indoor air quality management and the need for a comprehensive approach to reducing disease transmission in shared spaces.
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On March 27th, we proudly launched our video “Clean Air Matters”, created to raise awareness about the vital role of ventilation and air cleaning systems in reducing viral transmission in indoor spaces. This awareness film was made possible thanks to the creativity and efforts of the Oculus Film team.
Curious how the concept was brought to life on screen?
In our interview with Hans de Jonge, the film’s director, he shares insights into the creative journey, from translating invisible airflows into compelling visuals to striking a balance between science and storytelling.
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13 March 2025
MIST event 2 June 2025: Future of health-promoting ventilation and air cleaning systems
The MIST event 2025 brings together experts, policymakers, and the public to explore approaches to creating healthier indoor environments. Focusing specifically on schools, health centers, restaurants, offices, and public spaces, this gathering will showcase the initial outcomes of the groundbreaking MIST project.
Date: June 2, 2025
Time: 13:30 - 18:00
Location: Berlagezaal, Faculty of Architecture and Built Environment, Delft University of Technology
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05 February 2025
Importance of ventilation and/or air cleaning in relation to risk of indoor transmission of infectious diseases: Insights from Prof. Lidia Morawska
We are delighted to announce that Professor Lidia Morawska, a world-renowned expert in indoor air quality, will join us as a keynote speaker for the MIST event 2025 on June 2nd!
In a recent interview, Professor Lidia Morawska outlined evidence-based approaches for improving indoor environments through ventilation, effective air-cleaning technologies, and comprehensive monitoring systems.
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MIST Consortium Meeting 06 February 2024
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