Plenary IV
Friday, October 6th 11:00 AM – 12:15 PM

The role of aerosol science in understanding and minimizing the risk of airborne infection transmission

Session Abstract: The term “prevention of infection transmission” evokes in most people an image of a white-clad medical professional, shielded from head to toe in personal protective equipment, while disinfecting, testing, or performing medical procedures on infectious patients. But apart from physicists and other scientists working in this field, few people realise that in fact physics, and more specifically aerosol physics, plays a major role in infection transmission. The interdisciplinary nature of the process of infection transmission makes it an immensely complex and interesting area to study, but also opens the door to misunderstanding and misinterpretation.

Understanding the numerous physical mechanisms involved in infection transmission is critically important in lowering the risk of infection transmission; this is where aerosol science comes to the fore. Yet the broader role of aerosol science is to interact and communicate with other scientific fields, particularly the medical community, to facilitate an understanding of the physics of the process in the “languages” of these disciplines. When the physics is understood, appropriate risk mitigation measures can be implemented according to the roles and responsibilities of these disciplines.

The problems start with the definitions of aerosol science terms. Aaccording to aerosol science, an aerosol is defined as “an assembly of liquid or solid particles suspended in a gaseous medium long enough to enable observation or measurement” (Kulkarni et al. 2011). In contrast, medical science defines an aerosol as a small particle, while a droplet is a particle larger than 5 µm. Discussion about the terminology is still raging and dividing expert communities, so to help unite the fields, we propose to use the term particles, rather than aerosols or droplets, [Morawska and Buonanno, 2021].

But addressing the terminology is just the beginning. The next step is to develop a quantitative understanding of particle generation, particle emission, particle evaporation, particle flow dynamics, and particle disposition.

Particle generation occurs in the respiratory tract during human respiratory activities, which include breathing, speaking, singing, or coughing. After the particles are emitted, complex physico-chemical reactions occur as a result of particle evaporation in the air and flow dynamics drive the process of particle transport between the infected and a susceptible person. The final step is the disposition of the particles in the respiratory tract of the susceptible person, at which point the biological process of infection starts.

How well do we understand these processes? In our recent review on this topic [Morawska and Buonanno, 2021], we concluded that although the generation of particles in the respiratory tract is understood qualitatively, there is little quantitative knowledge about the characteristics of particles emitted during respiratory activities, their fate after emission, and their deposition during inhalation. More studies are clearly needed to address these knowledge gaps....

Speaker: Lidia Morawska is Distinguished Professor at the Queensland University of Technology in Brisbane, Australia, and the Director of the International Laboratory for Air Quality and Health at QUT, which is a Collaborating Centre of the WHO. Lidia also holds positions of Vice-Chancellor Fellow, Global Centre for Clean Air Research (GCARE), University of Surrey, UK and of Adjunct Professor, Institute for Environmental and Climate Research (ECI), Jinan University, Guangzhou, China. She conducts fundamental and applied research in the interdisciplinary field of air quality and its impact on human health and the environment, with a specific focus on science of airborne particulate matter. She is a physicist and received her doctorate at the Jagiellonian University, Krakow, Poland for research on radon and its progeny. An author of close to one thousand journal papers, book chapters and refereed conference papers, Lidia has been involved at the executive level with several relevant national and international professional bodies, is a fellow of the Australian Academy of Science and a recipient of numerous scientific awards, including L’Oréal-UNESCO Award 2023 for Women in Science. She was named one of TIME100 world’s most influential people for 2021, for her global leadership work on the importance of airborne transmission of SARS-CoV-2.

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