Engineers are making strides in reducing air pollution

February 27, 2015

According to the Environmental Protection Agency (EPA), the average adult breathes 3,000 gallons of air per day — yet the same air that fuels our bodies also can harm them. In fact, inhaling certain air pollutants can worsen conditions such as asthma, and studies estimate that thousands of people die prematurely each year due to air pollution.

Tracey Holloway, a University of Wisconsin-Madison professor with appointments in the Nelson Institute for Environmental Studies, civil and environmental engineering, and atmospheric and oceanic sciences, is tackling the very real problem of air pollution through her research and teaching at UW-Madison.

UW-Madison professor Tracey Holloway
Tracey Holloway

“I want to understand what is in the air we breathe and how is air pollution affected by energy uses, such as electricity use and transportation,” Holloway says. “I study air quality to inform both public health and public policy.”

In particular, Holloway focuses on health-damaging chemicals in the air, using computer models that have roots in engineering. The models use fluid dynamics equations to represent pollutants in the air. “The models help us estimate how energy choices affect the air. Like, if fewer nitrogen oxides were being emitted from cars, what would that mean for the number of smoggy days in a particular city,” Holloway says.

Her work revolves around understanding “if-then” relationships. She says computer models help inform cost-effective and health-beneficial solutions to air pollution.

Much of Holloway’s work examines how different energy sources affect air pollution. “A major reason we are trying to build better engines or power plants is to reduce the air pollution that comes from burning fossil fuels,” Holloway says. “It’s a natural fit to have someone like me, who is studying what is in the air and how it got there, along with engineers who are trying to build a cleaner engine or build a more efficient power system.” 

Holloway also focuses on air pollution transport on a global scale. “Air pollution does not stop at national or state borders,” Holloway says. “Estimating how much air pollution is going from one country to another requires computer models. A measurement of what is in the air doesn’t tell us where the pollution came from or where it’s going.”

For instance, Holloway says that with these types of models, she could "turn off" air pollution in China or the United States and see how it affects air pollution across the globe.

One area of particular interest to Holloway’s research team is the value of high-resolution models (with smaller grid-boxes) in understanding air chemistry. These models take longer to run on a computer — weeks or even months — but it can be worthwhile to see what is happening in cities versus suburbs, or in complex regions like the Lake Michigan coastline.

And sometimes, seeing the details really can change the big picture. For example, Holloway’s team found that emissions from Europe to Asia increased urban smog in coarser resolution (bigger grid boxes) models, but actually decreased urban smog when calculated with a higher-resolution model. While it seems surprising, Holloway says this is just what her team expected. “Cities have a lot of pollution, so the air chemistry is different than in cleaner areas. Outside of cities, nitrogen oxide creates ozone, but in polluted cities, nitrogen oxide can react with the ozone and actually reduce it. Coarser models can’t resolve the difference in urban versus non-urban chemistry, so this is a strength of our high-resolution modeling approach.”

A NASA satellite image shows the reduction in nitrogen dioxide levels in Chicago between 2005 and 2011
A NASA satellite image shows the reduction in nitrogen
dioxide levels in Chicago between 2005 and 2011.

Holloway submitted an amicus curiae (“friend of the court”) brief to the United States Supreme Court on the topic of state-to-state air pollution transport, when justices were considering rules about the Cross-State Air Pollution Rule in 2015. “My goal is to get better scientific information into the hands of decision makers so that they can be weighing these issues in terms of jobs, cost and health in light of the best information possible,” Holloway says.

One way Holloway achieves this is through her role as deputy director for the NASA Air Quality Applied Sciences Team (AQAST). The team works to make NASA’s advanced products relevant for air quality management. In particular, Holloway says NASA’s satellites are a great way to see certain chemicals in the air, especially those not visible to the naked eye, such as nitrogen dioxide.

“It is an amazing resource to have a snapshot of this pollutant that we can't see with our eyes but comes from all these major energy sources. We can see it over the whole world every single day through these satellites,” Holloways says.

For Holloway, engineers are major players in reducing air pollution. “Engineering is taking scientific tools and ways of thinking and applying them to real-world problems,” Holloway says. “Air quality is a real-world problem. It is a problem that links across a wide range of engineering disciplines and pretty much any engineering student with an interest in air quality can leverage his or her background to contribute to the discussion on making cleaner engines, cleaner air and healthier communities.”

Holloway also loves being part of a university that has so many strong programs.

“I think we are lucky that UW-Madison has such a great engineering program, but also that we have so many programs that are key to real-world problem-solving from communication to agricultural systems to science and weather,” Holloway says. “I think we are at a place where we can make a tangible difference in our world today.”

This story was originally published by the College of Engineering

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