Clearing the Air

For chemical engineer V. Faye McNeill, air quality and climate change go hand in hand. McNeill and her research team at Columbia investigate how to improve the predictive power of atmospheric chemistry and climate models, performing laboratory and modeling studies of the complex chemistry and physics of aerosols and ice in the atmosphere to better understand how human activities impact the environment.

Photochemical reactor used in the McNeill Lab to study aerosol chemistry under simulated atmospheric conditions (Photo by Jeffrey Schifman)

A key focus of their work centers on atmospheric aerosols—small particles suspended in ambient air, also known as particulate matter. They can be emitted directly into the atmosphere through sources like sea spray or a dust storm, but a large percentage of these particles develop from chemical reactions of gases in the atmosphere.

High levels of atmospheric aerosols are a hallmark of poor air quality, and they can negatively impact human health. These particles contain microscopic solids or liquid droplets that can get deep into a person’s lungs and aggravate asthma, increase preexisting respiratory infection symptoms, and decrease lung function. They can also lead to irregular heartbeat and heart attacks, difficulty breathing, and premature death in people with heart or lung disease.

However, these particles also play several important roles in Earth’s climate—serving as seed particles for cloud formation, and absorbing and reflecting the sun’s rays to produce a cooling effect, for example. “For this reason, air quality and climate should be considered together when decision makers develop environmental policies,” explains McNeill, associate professor of chemical engineering.

“Not all the sources of atmospheric aerosols are well known, particularly not in the case of particles formed from chemical reactions of atmospheric gases,” she says. “This makes predicting the amount and location of aerosols, and using those predictions to develop environmental policies, tricky. A large part of my group’s work focuses on unraveling these chemical pathways and determining how the particles’ chemistry may change their climate-relevant properties—such as color, which affects their ability to absorb light.”

McNeill explains that it’s a major challenge in atmospheric chemistry, climate studies, and other disciplines to bridge the scales between the large amount of detailed, molecular-level data researchers get in the laboratory and the coarse-grained information that large-scale models can handle. To meet this challenge, McNeill’s team developed the Gas Aerosol Model for Mechanism Analysis (GAMMA). It simulates the evolution of hundreds of chemical species participating in hundreds of chemical reactions, in both gas and particle phases, and the transfer of those molecules back and forth between the phases.

V. Faye McNeill (Photo by Jeffrey Schifman)

GAMMA analysis led her team to realize that, of those hundreds of species and reactions, only two main reaction pathways completely dominated their chemistry focus.

“This inspired us to develop a more coarse-grained version of GAMMA, called simpleGAMMA, which captures the overall behavior of the detailed model faithfully but has only a few variables and equations,” she explains. In this way, simpleGAMMA can be applied to large-scale models without adding a lot of computational complexity, or it can be used for analyzing field data with limited measurements.

McNeill and her team have partnered with several other research groups to implement simpleGAMMA in regional and global atmospheric chemistry and climate models. They’ve also used simpleGAMMA to analyze field data with their collaborators, especially from the Southern Oxidant and Aerosol Study, which took place in the southeastern United States in 2013.

“We collaborate with other groups in order to include our most significant findings in large-scale models of air quality and climate, thus improving their predictive power,” says McNeill. “This is how lab experiments eventually lead to better environmental policies.”

McNeill was initially motivated to study atmospheric aerosols as an undergraduate student at the California Institute of Technology.

“At that time, Los Angeles had a serious particulate pollution problem, and visibility was low almost every day,” she explains. “There were mountains very close to campus that we could only see a few days out of the year. In addition, I’ve had asthma my whole life, and I had difficulty breathing throughout my time living there. These daily reminders of the issue’s importance, together with the very elegant and exciting physics and chemistry of atmospheric aerosols, got me hooked.”

McNeill is eager to continue her timely research as worldwide efforts to address the threats of climate change increase.

“Atmospheric aerosols play an important role in global climate, and uncertainty in their sources is one of the biggest unknowns in climate predictions,” she says.

Prior to joining Columbia in 2007, McNeill was a postdoctoral research associate in the Department of Atmospheric Sciences at the University of Washington. In 2015, McNeill was awarded the Kenneth T. Whitby Award from the American Association for Aerosol Research, the Association’s highest honor for researchers in her career stage.

—by Jessica Driscoll

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