Carnegie Mellon University
June 11, 2014

Investigating Air Quality: CMU’s Center for Atmospheric Particle Studies

Investigating Air Quality: CMU’s Center for Atmospheric Particle Studies
Looks can be deceiving—even the clearest air is full of microscopic and even nano-sized particles. CEE/EPP Professor Peter Adams, the recently named director of CMU’s Center for Atmospheric Particle Studies (CAPS), and his colleagues are investigating where these particles come from, their effects on us, and their role in global climate change. 

According to Adams, CAPS is a “grassroots” collaboration of Carnegie Mellon faculty members who are interested in doing air pollution research. Major funders of the center include the EPA, Department of Energy, NASA, and the National Science Foundation, usually through grants often co-written by two or more members.  

The seven faculty members involved are Adams, Chemical Engineering/Chemistry Professor Neil Donahue, Chemical Engineering Research Professor Spyros Pandis, Mechanical Engineering Department Head and Raymond J. Lane Professor Allen Robinson, Assistant Professor of Mechanical Engineering and Chemistry Ryan Sullivan, Assistant Research Professor of Mechanical Engineering Albert Presto, and Assistant Teaching Professor of Mechanical Engineering, Satbir Singh. They represent five different departments in two colleges, making CAPS a classic example of Carnegie Mellon’s affinity for interdisciplinary collaboration.   

Though the center studies several aspects of air pollution and atmospheric chemistry, Adams says that the focus has been on PM (airborne particulate matter). PM can be both man-made, like exhaust particles from your car, and from natural sources, like mineral dust.  Sometimes, when certain gas molecules cluster together, new particles can even form spontaneously in the atmosphere. Adams says that though it’s not possible to see the particles individually, you can see evidence of their combined effects. “You know on a summer day when the horizon is white and hazy? That haziness is the collective effect of all of the particles, which are like a bunch of tiny mirrors scattering light.”

One reason that CAPS researchers are interested in studying PM is that it can have important implications for human health. According to Adams, PM can increase the likelihood of both lung cancer and surprisingly, heart attack. The second and equally important reason is that PM is thought to affect climate change.  Specifically, scientists think that the reflective properties of PM have mitigated global warming, perhaps reducing the amount of warming that has occurred by 20 to 80 percent.  As this is a huge range, CAPS researchers are working to better understand this phenomenon.

Adams’ role in this work involves building mathematical simulations of the way particles enter, interact within, and exit the atmosphere.  To do this, he first splits the atmosphere into a series of virtual 3D boxes.  In each box, his simulations track a variety of emissions—from power plants, cars, etc.—as they move through the air.  

“It’s basically a fancy way to map emissions into concentration,” says Adams. “After all the chemical reactions take place, what is someone downwind going to breathe?”

By modeling theoretical emissions reductions, he can help determine what regulations would be most effective for improving air quality. In addition to generating policy recommendations, Adams and his team use their expertise to improve the representation of PM in global climate models.  

But Adams’ research is only part of the PM investigation at CAPS, and in many projects, faculty members combine their expertise in experimental work, air quality measurements, computer modeling, and policy. He says that this kind of close collaboration often leads to better research. “When you can talk to people across the table, you can more easily bridge all the methodological gaps.”

He also believes the center’s diverse pool of faculty have deepened his understanding of his own research, and feels fortunate to have the opportunity to work in such a unique environment. “I can’t imagine doing this research without all of these colleagues around me.  It would be far less fun, meaningful, and impactful,” he says.  
Air Particles - EuropeTop: high-resolution (0.5 x 0.667 degrees) nested European grid. 
Bottom: close-up over Europe of the 4x5 grid. 

New Computer Cluster Allows for Improved Models

In Fall 2013, CEE, Engineering and Public Policy and Chemical Engineering funded a new computer cluster for CAPS researchers.  The new cluster contains 96 cores—a massive increase in processing power compared to the standard 1-4 core single computer.  Because complex computations can be spread out and run simultaneously over these cores,  “simulations that used to take us three months to run now take only a few days,” says Adams. In addition to producing faster results, the new cluster also allows him to run better simulations. “When you split the atmosphere into sections to be modeled, you want those sections to be as small as possible.  With this improvement in computer speed, we’re looking at improving the resolution by a factor of 100. It’s absolutely game-changing.”   

Image: European model shows the average number of particles for the first week of july 2005 with a diameter larger than 100nm per cubic centimeter. The model used is GEOS-Chem v.9-02, with TOMAS aerosol microphysics. The top model shows what the increase in computing power allows researchers to view vs the coarser grained view (bottom) that the previous cluster generated.

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