Scientists at the University of Birmingham, UK, have used physics-based modelling to develop a tool that lets cyclists and pedestrians visualize certain types of pollution in real time – and take steps to avoid it. The scientists say the data behind the tool could also guide policymakers and urban planners, helping them make cities cleaner and healthier.
As well as the exhaust from their tailpipes, motor vehicles produce particulates from their tyres, their brakes and their interactions with the road surface. These particulate pollutants are known health hazards, causing or contributing to chronic conditions such as lung disease and cardiovascular problems. However, it is difficult to track exactly how they pass from their sources into the environment, and the relationships between pollution levels and factors like vehicle type, speed and deceleration are hard to quantify.
Large-eddy simulations
In the new study, which is detailed in the Royal Society Open Science Journal, researchers led by Birmingham mechanical engineer Jason Stafford developed a tool that answers some of these questions in a way that helps both members of the public and policymakers to manage the associated risks. Among other findings, they showed that the risk of being exposed to non-exhaust pollutants from vehicles is greatest when the vehicles brake – for example at traffic lights, zebra crossings and bus stops.
“We used large-eddy simulations to predict turbulent air flow around road vehicles for cruising and braking conditions that are observed in urban environments,” Stafford explains. “We then coupled these to a set of pollution transport (fluid dynamics) equations, allowing us to predict how harmful particle pollutants from the different emission sources (for example, brakes, tyres and roads) are transported to the wider pedestrian/cyclist environment.”
A visible problem
The researchers’ next goal was to help people “see” these so-called PM2.5 pollutants (which, at 2.5 microns or less in diameter, cannot be detected with the naked eye) in their everyday world without alarming them unduly and putting them off walking and cycling in urban spaces altogether. To this end, they developed an immersive reality tool that makes the pollutants visible in space and time, allowing users to observe the safest distances for themselves. They then demonstrated this tool to members of the general public in the centre of Birmingham, which is the UK’s second most populous city and its second largest contributor to PM2.5 emissions from brake and tyre wear.
The people who tried the tool were able to visualize the pollution data and identify pollutant sources. They could also understand how to navigate urban spaces to reduce their exposure to these pollutants, Stafford says.
“It was very exciting to find that this approach was effective no matter what a person’s pre-existing knowledge of non-exhaust emissions was, or on their educational background,” he tells Physics World.
Clear guidance and a framework via which to convey complex physicochemical data
Stafford says the team’s work provides clear guidance to governments, city councils and urban planners on the interface between road transport emissions and public health. It also creates a framework for conveying complex physicochemical data in a way that members of the public and decision-makers can understand, even if they lack scientific training.
“This is a crucial component if we are to help society,” Stafford says. Longitudinal studies, he adds, would help him and his colleagues understand whether the method actually leads to behavioural change for vehicle drivers or pedestrians.
Looking forward, the Birmingham team aims to reduce the computing complexity required to build the model. At present, the numerical simulations are intensive and require high-performance facilities to solve the governing equations and produce data. “These constraints limited us to constructing a one-way virtual environment,” Stafford says. “Techniques that would provide close to real-time computing may open up two-way interactions that allow users to quickly change their environment and observe how this affects their exposure to pollution.”
Stafford says the team’s physics-informed immersive approach could also be extended beyond non-exhaust emissions to, for example, visualize indoor air quality and how it interacts with the built environment, where computational modelling tools are regularly used to inform thermal comfort and ventilation.
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