Understanding the behavior of microscopic aerosols expelled during coughing or sneezing has never been more critical, especially in light of ongoing global respiratory disease challenges such as influenza, COVID-19, and tuberculosis. These tiny particles, often invisible to the naked eye, serve as carriers for pathogens, enabling virus and bacteria transmission through the air. Numerous factors influence how these infectious aerosols disperse, including the strength of the exhalation, the intricacies of human respiratory anatomy, and environmental conditions. Recent groundbreaking research from the Universitat Rovira i Virgili (URV) has uncovered another vital element governing aerosol behavior: temperature. This revelation could transform how we understand and mitigate airborne disease spread indoors.
The research team from URV has demonstrated through meticulously controlled experiments that the temperature difference between exhaled air and the surrounding environment plays a significant role in the dispersion pattern and concentration of aerosols. Specifically, when warm exhaled air—mimicking body temperature—is introduced into cooler ambient air, the aerosol cloud maintains higher particle concentrations and travels further distances compared to situations where the temperature disparity is minimal. This relationship becomes more pronounced with increasing temperature gradients, shedding new light on the physical dynamics operating during respiratory emissions.
Central to this innovative study is the use of a sophisticated, three-dimensional-printed human airway model developed by the URV’s ECoMMFiT research group. This device replicates the biomechanics of human exhalation with exceptional stability and precision, allowing the researchers to simulate coughing and sneezing under tightly controlled parameters. By modifying this simulator to heat the exhaled air to 37 degrees Celsius—representing a slight fever condition—the team was able to explore interactions between temperature, respiratory flow dynamics, and aerosol dispersal in unprecedented detail.
Experiments were conducted within a climate-controlled chamber at the Catalonia Institute for Energy Research (IREC), where environmental conditions could be precisely manipulated. The team investigated three distinct ambient temperatures: 27°C, 17°C, and 7°C. These temperatures were combined with varying exhalation intensities and two different modes of nasal airflow: open and closed nasal cavities. This combination resulted in eighteen unique trial configurations, each rigorously repeated ten times for statistical robustness, culminating in a comprehensive dataset derived from 180 individual experiments.
The results reveal that the aerosol clouds generated under these varying conditions behave differently in predictable yet complex ways. As Nicolás Catalán, co-author and URV mechanical engineering researcher, explains, the increased temperature difference augments buoyancy effects. Warm exhaled air, less dense than the surrounding cooler air, rises and carries aerosol particles further and more cohesively. This buoyant lift sustains particle concentrations for longer periods, significantly extending the spatial range of potential pathogen transmission, particularly in colder environments.
A particularly striking finding relates to the role of the nasal cavity in shaping aerosol spread. The study confirms that partial airflow through the nose reduces horizontal propagation but promotes increased vertical dispersion. Conversely, when the simulator mimics mouth-only exhalation, aerosols tend to move more horizontally, covering greater frontline distances. This mechanistic insight highlights how variations in individual respiratory behaviors and anatomical structures can dramatically impact transmission risks.
The technical prowess of the study owes much to the utilization of high-speed videography and laser illumination techniques. These tools unveil the fine-scale structure and temporal evolution of the aerosol clouds. The recorded visualizations underscore how the interplay between ambient temperature gradients and respiratory airflow generates intricate aerosol flow patterns. This mechanistic understanding is crucial for modeling pathogen transport pathways more accurately within indoor environments, where interventions are typically applied.
Notably, the research contributes valuable experimental data that historically has been scarce in aerosol studies. Previous investigations frequently relied on numerical simulations or human trials, each limited in their control over parameters such as flow rate and temperature. In contrast, the URV’s 3D-printed airway simulator enables reproducible and stable experimental conditions, providing crucial validation points for computational fluid dynamic (CFD) models that predict aerosol dissemination and, by extension, infection risk.
From a practical standpoint, these insights hold significant implications for public health and safety. Environments like hospitals, schools, biological labs, and public transportation systems, where pathogen exposure risk is elevated, can benefit from refined ventilation designs and tailored control measures based on thermal considerations. For example, in colder seasons or cooler indoor environments, the increased persistence and reach of respiratory aerosols could warrant enhanced air circulation strategies or modifications to heating systems to mitigate transmission potential.
While the research sheds new light on temperature’s role in aerosol dynamics, the authors caution that respiratory aerosol behavior is inherently multifaceted. Factors such as humidity, indoor ventilation patterns, and the longevity of suspended particles must be further investigated to achieve comprehensive risk assessments. The study encourages continued interdisciplinary research integrating experimental, computational, and epidemiological approaches to fully unravel the variables influencing airborne disease propagation.
The research team’s approach, combining experimental rigor with innovative simulation, establishes a robust framework for future investigations. Their novel use of a temperature-controlled exhalation model advances the field beyond simplistic or static assumptions about aerosol dynamics. This detailed analysis forms a foundational step towards predictive models capable of informing adaptive infection control protocols sensitive to thermal variances across seasons and indoor spaces.
In conclusion, the URV-led study emphasizes that temperature differences between exhaled and ambient air significantly affect bioaerosol transport, influencing both the extent and persistence of pathogen-laden particle clouds. By integrating anatomical realism through a 3D-printed airway model and employing precise climate control, the research advances our scientific understanding of respiratory aerosol physics. These findings promise to inform smarter environmental and public health strategies, reducing airborne transmission risks in indoor settings worldwide.
Subject of Research: Respiratory aerosol dynamics and pathogen transmission influenced by temperature differences.
Article Title: Bioaerosol transport dynamics in cold and warm environments: An experimental study using a three-dimensional-printed human airway model.
News Publication Date: 20-Mar-2026
Web References: http://dx.doi.org/10.1063/5.0303143
References:
Catalán, N., Cito, S., Varela Ballesta, S., Fabregat, A., Vernet, A., Graus, D., & Pallarès, J. (2026). Bioaerosol transport dynamics in cold and warm environments: An experimental study using a three-dimensional-printed human airway model. Physics of Fluids.
Keywords
Respiratory aerosols, airborne pathogens, bioaerosol transport, temperature effects, human airway model, aerosol dispersion, exhalation dynamics, infectious disease transmission, ventilation, computational fluid dynamics, public health, indoor air quality
