CAPS investigates causes and implications of air pollution

Air pollution has been a huge problem over the past century, especially here in industry-based Pittsburgh. But beginning last summer, a team of researchers at Carnegie Mellon have conducted research on particle air pollution and reevaluated the effect of these particles on health and the environment.

The Environmental Protection Agency (EPA) has attempted to reduce pollution through specific concentration limits. Air pollution in particular has always been an issue, requiring costly solutions and causing roughly 50,000 premature deaths in the U.S. yearly. It has also been proven to have a negative effect on climate around the globe.

Neil Donahue, a professor of chemistry, chemical engineering, and engineering and public policy (EPP), helped spearhead the project due to his interest in how chemicals are oxidized in the atmosphere. He and Allen Robinson, a professor of mechanical engineering and EPP, belong to Carnegie Mellon’s Center for Atmospheric Particle Studies (CAPS), which helped conduct the study.

Over the past few years, Donahue's goal has been to work with a team of scientists and engineers in order to answer two questions about air pollution: Where do these particles come from, and what are their influences on climate and public health?

CAPS involves around 50 people, including both graduate and undergraduate students, post-doctoral scientists, research manager Albert Presto, and engineering professors Peter Adams and Spyros Pandis. They based their research off of work previously done by a group at the University of Colorado, who wrote a paper describing what several of the air particles looked like.

CAPS’s work began in the laboratory, using smoke-emitting devices like diesel engines and wood stoves. The emissions are diluted to atmospheric conditions inside a large Teflon bag. Afterward, the bag was exposed to ultraviolet light that acts as a model for the sun, causing a burst of chemical reactions inside the bag. The resultant organic substances were analyzed with mass spectrometers.

The research soon moved into the field. Last summer, the group visited Pittsburgh International Airport and put the emissions from their 737 engines through the same test. Additionally, they traveled to Montana and the National Fire Laboratory to test smoke from forest fires. A press release from [SLANT12][SLANT12] stated that CAPS now has the ability to perform air quality research directly in the area of interest: "The team harnessed new technology — a custom-outfitted box truck with on-board instruments that allow researchers to conduct experiments at places where the pollution exists, rather than having to take everything back at the lab."

Air pollutant particles affect water droplets in clouds. The higher the particle numbers in the atmosphere, the denser the cloud (resulting in the clouds appearing whiter than normal). Dense clouds reflect sunlight at a greater percentage than other clouds, resulting in an overall “cooling effect” on the planet. The change in “[solar] energy due to changes in clouds between 1850 and now is one of the largest uncertainties in climate models,” said Donahue.

Air pollutants may also find ways to return to the surface of the planet, but the form may have huge consequences. Using a one kilogram bottle of Pennzoil, containing thousands of potentially harmful organics, as an example, Donahue explains that if the oil were allowed to spread across Carnegie Mellon’s entire campus, it would evaporate, and there would be about one microgram of the pollutant per every cubic meter of air. Although diluted enough to meet EPA standards, CAPS research has shown that the oil in gas form can be transformed, condense onto particles, and contribute to particulate pollution in what Donahue calls “reactive distillation.” These new, oxidized molecules have very different effects on clouds and probably have very different health effects (an area of current research).

This transformation also means more bad news. It may mean that scientists have underestimated the effect of certain pollutants on the environment, since they’re transformed into entirely new substances after they enter the atmosphere. The new substances affect the chemical pathways that cause climate change and have other adverse effects, meaning that new green technology, such as revamped catalytic converters in cars and diesel particulate filters in factories, might need to be reevaluated. “Is [green technology] going to solve our problem?” wondered Robinson. “Maybe not.”

Donahue, Robinson, and the rest of the team will continue their work later this year by analyzing vehicle emissions in Los Angeles. With the data they’ve compiled, they hope to reach new conclusions on how we affect our planet.