Research on Infectious Aerosols

This research program has been led by CBE faculty and researchers in collaboration with affiliated researchers and research institutions around the world.

Study on the Use Ceiling Fans Indoors to Reduce the Risk of Transmission of Infectious Aerosols

The effects of ceiling fans on the transmission of infectious aerosols remain poorly understood, leading to conflicting recommendations. To address this gap, we conducted experiments in a controlled chamber with a typical mixing ventilation system at various ventilation rates, with and without ceiling fans, measuring tracer particles at various locations. Results show that with ceiling fans, tracer particles were distributed more homogeneously throughout the room, leading to up to 77 % reduction in short-range particle exposure, while a slight increase of less than 14 % in long-range exposure. Based on the dilution factors obtained from the experiments, we developed a decision making tool that uses the ventilation rate, the number of individuals at short- and long-range, and the disease’s transmissibility to decide whether the use of ceiling fans is beneficial.

Effectiveness of Triethylene Glycol Disinfection of Airborne Microorganisms Under Diverse Building Operational Parameters

Research on triethylene glycol (TEG) use to disinfect airborne microorganisms was previously conducted in non-realistic chamber settings. We carried out a study to evaluate how air temperature, humidity, HVAC settings and filtration affect TEG’s effectiveness in deactivating MS2 bacteriophage, a common surrogate for SARS-CoV-2, in a simulated office-sized chamber. Results show that TEG’s efficacy declined with the increase in temperature from 72 to 77°F (22.0 to 25.0°C), it was higher at 55 % RH compared to 40 % and 70 %, it increased with higher recirculation rates, but decreased with higher ventilation rates and more efficient filters. Our results suggest that the optimal conditions for TEG performance are with air temperature of 72 or 74°F (22.0 or 23.5 °C) , 55 % relative humidity, 0.8 ACH ventilation rate, and 6 ACH recirculation rate. Findings also suggest a possible risk of overestimating the benefits of combined solutions. Results of the journal paper are summarized in this post.

Diurnal Trends of Indoor and Outdoor Fluorescent Biological Aerosol Particles in a Tropical Urban Area

Bioaerosols, representing up to 15–70% of atmospheric particulate matter (PM), are of high interest due to their effects on human health and their role in climate and atmospheric science. At sampling sites located inside and on the rooftop of a high-rise commercial building in Singapore, we conducted a ten-week continuous sampling of bioaerosols. We documented diurnal trends of bioaerosol concentrations, both indoors and outdoors, which can help people, especially more susceptible individuals, to reduce their overall exposure. We also found that the HVAC system dislodged the overnight-settled and accumulated fine bioaerosols into the indoor environment. A detailed report can be accessed here  and in this journal version.

Size-Resolved Dynamics of Indoor and Outdoor Fluorescent Biological Aerosol Particles in a Bedroom

We evaluated the interrelations between indoor and outdoor bioaerosols in an occupied bedroom. Two wideband bioaerosol sensors were used to measure indoor and outdoor particulate matter (PM) and fluorescent biological airborne particles (FBAPs), which were within a size range of 0.5-20 μm. Results reported in this journal paper show that human or human-related activities were the major indoor sources of bioaerosols, while non-biological particles come from outdoors. From this study, we show that opening or closing a window is a simple and effective way to lower indoor bioaerosol exposure. Whether we should keep the window open or closed can be based on the outdoor PM level and indoor activities. Together, this can inform occupants about window opening practices, and to inform the operation of windows that open or close automatically.