This summer, a team of students in the Department of Chemical Engineering & Applied Chemistry (ChemE) at the University of Toronto is taking on an important question: What are we breathing when we ride the subway and does it affect our health?
The SAUCE study — short for Subway Aerosol Urban Commuter Effects — builds on previous research exploring air quality in Toronto’s subway system, specifically focusing on Line 2 (Bloor–Danforth), and represents a new phase of the research. In collaboration with Professor Chung-Wai Chow from the Faculty of Medicine, who is also cross-appointed to ChemE, the team — which includes second-year ChemE undergraduate students Cesar Andres Siu Elvir and Alisha Bangari, and ChemE PhD student Nicole Trieu among others — will evaluate whether riding the subway produces detectable respiratory changes in healthy individuals.
The goals of the study include determining whether there are any immediate respiratory changes in individuals after approximately two hours of subway travel; evaluating the performance of low-cost sensors in measuring particulate matter concentrations on the subway, in order to determine if commuters could use them to determine their own exposure; and assessing whether the air quality on Line 2 has changed since previous studies. The team is also interested in understanding how external events, such as wildfires, might influence air quality in the subway system.
“The subway offers a unique and often overlooked environment for air quality research,” says Elvir.
“Although public transit plays a crucial role in building sustainable cities, the air inside subways isn’t regularly monitored or well understood — even though some commuters spend several hours a day in transit.”
The students also point out that air quality on Line 1 (Yonge–University) is noticeably better than on Line 2. This variation makes Line 2 a particularly important area to study. Their findings could help inform how future transit systems — such as the upcoming Ontario Line — are designed, including decisions around train technology, ventilation systems and better overall standards for public transit infrastructure.
How is the research set up?
Two teams of three students each take turns riding the subway to monitor air quality using three low-cost sensors and a particulate matter sampler. Each student carries the equipment in a medium-sized backpack and small luggage bag, making the setup portable and easy to place on subway seats. Throughout the 1.5 to 2-hour journey on Line 2, they collect time-specific particulate matter at 2.5 mass concentration and total mass concentration data.
“The data collected is a series of oscillatory and spirometry results from each individual subject,” says Elvir.
“All of the sensors we carry in the pilot study are meant to monitor and determine the air quality of the subway. They are categorized into three connected purposes: gravimetric analysis, chemical composition of the subway air and optical continuous particulate matter mass concentration monitoring.”
The students perform oscillatory and spirometry tests before the subway trip and immediately after their last stop.
“The Oscillometry tests are used to determine airway resistance at different frequencies, whereas spirometry tests are simple lung function tests used for monitoring lung function over time,” says Bangari.
“The tests aim to accurately measure any respiratory changes from the commute.”
Some of the sensors used in the SAUCE study were previously introduced to second-year chemistry students in a course called CHE230 Environmental Chemistry.
“In this course, students conduct group projects using these sensors to measure air quality in various environments,” says Professor Arthur Chan (ChemE), who teaches the course.
“Not only are they extending their learning beyond the classroom through SAUCE, but these students are also helping us improve the student experience in future CHE230 projects, by testing out sampling and data analysis protocols, and developing learning materials that will connect knowledge gained from the different courses in 2nd year.”
Students’ roles this summer
Elvir is responsible for quality assurance and control of the devices, ensuring they are properly calibrated and ready for use before each trip.
“Besides calibrating and preparing devices, I download and analyze some of the data collected from the optical mass concentration sensors by identifying particulate matter spikes at specific timestamps and calculating indoor/outdoor ratios,” he says.
“I am also participating as one of the subjects going on the subway.”
For Bangari, the experience has provided an opportunity to connect her technical studies to real-world health and environmental issues. “My role in the SAUCE study is to participate in the subway trips and perform lung function tests,” she says.
Trieu, who previously worked on related studies sampling across Lines 1, 2, and 4 during her PhD research, is overseeing the campaign. “This summer, I am designing and overseeing the subway sampling campaigns and mentoring the summer student team,” she says.
“I’m most looking forward to seeing if the unique composition of subway PM2.5 translates into detectable respiratory changes — something we haven’t yet quantified in our previous work.”
Public engagement and broader impact
Public engagement is an important part of the project. The team notes that Toronto’s subway air quality information is vital for the city, and there is not enough easy-to-access information about how “healthy” the subway is. They hope to reach not only commuters, but also environmental groups, transit agencies and communities in other cities who may be inspired to investigate their own transit systems.
Bangari highlights her efforts to share the team’s work publicly. “I created an Instagram page for SAUCE to let people know about our research objectives and aims. I have also uploaded a few informative posts about what our study aims to address, as well as a short video on how a typical subway journey looks like for summer students participating in the research.”
For all of the students participating in the SAUCE study this summer, including Isaac Lo (Chem), Nicholas Ali (EngSci) and Jieun Kim (ChemE), the project has been a meaningful way to apply their engineering skills to real-world impact.
“As a chemical engineering student, getting to apply knowledge that I learned in second year is helping me understand how theoretical concepts are used in a real-life context,” says Elvir. “This research is a step into achieving my career goals in environmental engineering and energy.”
Bangari echoes this sentiment. “Being a part of this research team is very meaningful because it provides an opportunity for me to bridge my technical background with real-world environmental health challenges,” she says.
“Through this research, I apply my knowledge in air pollution and health effects of particulate matter to investigate human exposure in everyday settings. I am excited to be part of a research project where my contributions have the potential to create positive impacts, which is one of the main reasons why I chose to join chemical engineering in the first place.”
As the pilot progresses, the students are aware of the challenges that lie ahead — including instrument malfunctions, subway delays and the physical demands of the medical testing. Still, they’re motivated by the opportunity to contribute to both science and society.
“The thing I am most looking forward to is how our efforts and influence on this research study can impact other people’s lives,” says Elvir.
“I want to see the hopefully positive impact this study can do in Toronto and see changes happening in the long term, from the perspective of a commuter myself.”
Follow the ChemE and SAUCE Instagram accounts for exclusive insights and updates on the team’s research.
EDIT: August 22, 2025: SAUCE Study researchers & Prof. Greg Evans interviewed by CityNews