Clearing the Air: Tami Bond’s Computer Model Is Best Forecast Yet on Policies Aiming to Control Soot

posted: 5/8/2019
Hertz Staff
listed in Fellows

In the February 11 issue of Nature Sustainability, a multi-institution team unveiled a new tool for understanding and controlling the health and climate impacts of shipping goods – a source not only of greenhouse gases but of soot and smog threatening our health.

In the journal, Hertz Fellow Tami Bond (’95), Professor of Civil Engineering at the University of Illinois, and her team presented an extensive computational model of the environmental impact of the American shipping industry. Unprecedented in its complexity, the model connects everything from the chemical intricacies of diesel exhaust to the geography and economics of our truck-dependent shipping infrastructure.

Using the model to predict the warming and health impacts of American freight over the next 30 years, the team pointed to three policies which, applied over the coming decades, could save up to 4,000 lives per year and cut the warming contributions of our shipping by a quarter.

The policies included a carbon tax ramping up to $100/ton over the next 30 years, compliance with existing maintenance regulations, and more compact urban development. The results showed that existing efficiency regulations will save up to 3,000 lives per year by 2050, and perfect compliance could save up to 1,000 more. The carbon tax, provides the vast majority of climate benefits, reducing both long- and short-term warming by nearly a quarter by itself.

According to Bond, the study provides not only useful predictions of the impacts of these three policies, but also a model that can be adapted and reused to inform other policy choices. “We designed this so it would be easy to run many more scenarios,” she said. “This way if people wanted to change things or explore assumptions, we’ve added the flexibility to do this.”

“We designed this so it would be easy to run many more scenarios. This way if people wanted to change things or explore assumptions, we’ve added the flexibility to do this.”

Recently, Bond discussed what is unique about this new model, how it can affect policy decision making, and the impact of pollution caused by the soot generated by the transportation industry. The edited conversation is below.

Greehouse gas emissions from trucks
Photo by Ken Lund. cc-by license
CO2 isn't the only greenhouse gas trucks like these emit. Tami Bond studies how their complex fumes affect our health and climate.

HERTZ FOUNDATION: Anyone who drives on a highway is familiar with the black exhaust that comes out of a truck, but not everyone appreciates the environmental impact of this type of pollution. Why exactly does this matter?

Bond: This soot – which we call black carbon – absorbs sunlight very effectively, trapping its heat in our atmosphere, so it’s a significant contributor to Earth’s warming, especially in the year after it’s emitted. And in the United States, a lot of this soot is coming from transportation – more specifically, diesel engines, because they make more black carbon compared to gasoline engines. Especially in the United States, where we don’t have much passenger diesel, most of the diesel engines are used in freight. Policies that reduce freight activity will help both the long-term warming of CO2 and the short-term warming of black carbon.

"Policies that reduce freight activity will help both the long-term warming of CO2 and the short-term warming of black carbon."

Your team’s new model vastly improves predicting the health and environmental impact of policy decisions overseeing the transport industry. What exactly is different about your model?

Models that typically estimate the environmental impact of the transportation industry do it by looking at population sizes, income, and how much goods are being purchased, But they don’t consider what kind of things people are actually buying, and what people are buying determines how it gets to them, whether it’s shipped by fuel-efficient trains or inefficient planes. To accurately reflect this, we dug deeper – better understanding what was being shipped and how, which depends a lot on value and weight. For example, coal is heavy and it’s cheap, and so nobody ships it by air, but iPods are expensive and light, and they typically go in airplanes.

Our model considers decisions like this, which matter a lot. We also captured the complex effect of a carbon tax on rail traffic – rail activity would increase if people move to a more fuel-efficient mode of transportation but decrease as they ship less coal and petroleum products.


Many policies are on the table for reducing CO2 emissions. Bond and her team examined the impacts of three, one already in play and two under discussion. A set of regulations that require truck engines’ fuel efficiency to be maintained throughout their lifetime is already on the books – the study’s baseline showed that this will improve emissions dramatically by 2050. The study also explored the impact of enforcing these standards perfectly, which would improve things still more, and of two other potential policies: a carbon tax and more compact urban development. The carbon tax they considered increases linearly over time, capping out at $130/ton of CO2 in 2050. The urban development policy they examined assumed cities grew denser faster than they otherwise assumed. Finally, they examined the impact of exploring all three policies together.

Your team included experts ranging from air chemistry to economics. How did you get such a diverse group to work together effectively?  

It was kind of a matter of putting experts in all these different areas in a box and shaking them until something came out. It helped that everybody who contributed was an expert in what they did, whether they had developed it from the ground up or whether they were already a user of that model. It prevented us from making some of the silly mistakes that can happen when you’re using a model that you’re not familiar with.

What do your results tell us about which policies might lead to a cleaner world and healthier life?

One positive takeaway comes from the “durability” regulations that require vehicles to have low emissions not just when they are purchased but 50 thousand or 80 thousand miles down the road. By reducing emissions over the long lifetime of these vehicles, these regulations have a really positive effect – they prevent over 2,000 deaths from pollution a year! This was something that many people didn’t want to do and that we’re still struggling to enforce, but I think that there's been a win. This shows we already know how to make change.

"This was something that many people didn’t want to do and that we’re still struggling to enforce, but I think that there's been a win. This shows we already know how to make change."

But there’s also a warning: many improvements don’t happen because the infrastructure wasn’t in place. For example, it takes decades to build up railway infrastructure, so that means that moving to more efficient rail shipping years in the future means we have to start improving our rail networks now.

You trained as an engineer, but this work goes well beyond that. How does work like this interact with someone, say, designing a better engine?

I think engineers are really good at designing for constraints, but they’re not quite as good at imagining what are those constraints.

Part of my role as an environmental researcher now is to help figure out two kinds of constraints. First, there’s the personal level: I look at what kinds of stoves or engines or transportation service people need, and how they decide what to use. And then I look at the global or societal level, considering things like how quickly we need to reduce emissions to protect human health and welfare.

Then the role of an engineer is to design for all of those constraints. And we’re very good at that, so we should be able to handle adding on something like reducing emissions. But that may need you to think more creatively – rather than just making combustion more efficient, you may need to completely rethink how you’re providing energy.

What does this tell us about what we as individuals can do?

Buying a hybrid car or using a cloth grocery bag are wonderful things to do, but they’re just small drops in a bucket. Most of us, as individuals, can’t build a rail network.

The first thing we need to do is have a national conversation about how to make these big changes – changes that require new infrastructure, projects that last beyond one election cycle. And second, we need to vote for people who aren’t afraid to think big. We need people who can start these projects, and see them through, within the system we have.

–Bennett McIntosh