One of the most dramatic symptoms of our changing climate is the increase in the frequency and intensity of wildfires. Leaving trails of carnage in their wake, wildfires cause around $50 billion in damage each year. But the fires are not just indicators of a warming planet. Their emissions also shape the climate system in ways that scientists are just beginning to understand.
Greg Drozd, an assistant professor of chemistry, is shedding light on how the emissions released by wildfires alter the earth’s system. This is urgent work. Understanding the impact that an increase in wildfires could have on the climate is crucial. Plus, as the smoke from the Canadian fires that choked the East Coast has underlined, we can no longer ignore the health effects of the emissions.
“The problem will continue,” said Drozd. “And atmospheric chemistry has now advanced to the point where we are able to think about the fuels coming out of forest fires on a molecular level, in terms of what they do to the climate and our health.”
Along with soot—essentially carbon dust—forest fires release organic molecules that absorb UV light. These compounds, some of them toxic, are part of a complex mixture known as brown carbon. As the brown carbon molecules absorb light, the light energy is converted to heat. “In the same way,” said Drozd, “as asphalt gets hot on a summer day.”
When those compounds make their way into a cloud, we have a problem. “Bright fluffy clouds reflect sunlight back out to space,” he said. “That is essentially cooling, because they prevent that light from coming in. Now if these brown carbon molecules from a forest fire wind up in a cloud, they absorb a small fraction of the light. Globally, that can add up to a warming effect.”
But the story does not end there. After exposure to sunlight, those brown carbon molecules begin to degrade, losing their color. “It’s like if you put a cover on your car, it fades in the sunlight. We call it photobleaching.” And when the brown carbon molecules fade, they lose their warming effect.
To ensure our climate models are as accurate as possible, we need to know how wildfires affect the climate. That means we must understand the speed of the photobleaching process. “But this is lesser known,” Drozd said. “What is the actual rate of this photobleaching? How accurately can we predict it? And what environmental factors might affect it?”
Drozd’s lab is making important discoveries. The story of brown carbon compounds, from their release in a fire to their integration into the atmosphere, is, it seems, more complex than previously thought. In results presented at the Gordon Research Conference on Atmospheric Chemistry in Newry, Maine, in August, Drozd found that brown carbon endures after the photobleaching process. “The molecule absorbs light. Then, through a series of reactions, it goes right back to where it started,” he said. “It doesn’t degrade. And often, it forms another larger molecule that seems to be more stable, that is still absorbing UV light.”
A regeneration mechanism, a recycling process, may be at work. This implies that we might have underestimated brown carbon’s climate impact. Our models, it turns out, may need updating.
From Ohio to Maine
Drozd is from Dayton, Ohio, and joined Colby in 2017 after a postdoc at the University of California at Berkeley. Coming to Colby was like coming home.
“I’ve known Waterville my whole life,” he said. His aunt, Joan Sanzenbacher, worked in College administration for many years. Every other summer, his family would drive from Ohio, camping along the way. Once in Maine, they would all go hiking.
The landscape is ingrained in him. These experiences fostered a deep love for the natural world. “The outdoors always meant a lot to me. That’s how I got into environmental chemistry.” As an undergraduate at Ohio State, he studied soil chemistry. But atmospheric chemistry, which was starting to become high profile, drew him in.
He became intrigued by how emissions from environmental disasters affect the climate and our health. Before working on wildfires, Drozd studied the atmospheric chemistry of oil spills.
As the oil sits on the surface of the ocean in the sun, it evaporates. It then turns into smog, which can travel up into the ozone, affecting the climate, and is detrimental to health. From planning clean-ups to protecting sea life, understanding how quickly oil evaporates under different conditions is crucial.
Over the last few years, Drozd has been simulating crude oil spills in his lab. Placing thin films of oil inside a 10-foot wind tunnel, and under an LED sun simulator, Drozd sheds light on how the coupling of wind and sun affects the chemistry of oil after it is released into the environment.
The brown carbon compounds emitted by wildfires, Drozd realized, could be studied in a similar way. First, Drozd takes brown carbon molecules, which are produced in a U.S. Forest Service lab in Georgia that simulates wildfires. Then, he dissolves them in solvent and simulates sunlight with an arc lamp, a technology, once used for movie projectors, that produces high-intensity UV light.
Couldn’t he just put the mixture outside? “You need a controlled experiment,” he said. “As soon as a cloud moves across the sky, everything changes.”
The solar spectrum varies across time and place. To account for this, Drozd also uses LEDs that break up the light into seven different ranges. This allows him to mimic sunlight in different parts of the world, at different times of the year, over the course of a day. “Imagine a nice piece of audio equipment. You can adjust all your levels: your bass, your mid, your treble,” he said.
“By measuring each individual effect of each part of the spectrum, we can adjust the levels to mimic sunlight. So as the solar spectrum changes, we can just dial in the effect of each range, and then we reproduce exactly what we want. We can dial it in for each day of the year.”
The question of wildfire emissions is a pressing one. But forest fires, Drozd has found, are also a dynamic way to introduce students to chemistry. Undergraduates are often put off by chemistry’s symbols and equations. So in his course Physical Chemistry: Thermodynamics and Kinetics, Drozd introduces students to the modeling of chemical processes by getting them to predict a forest fire’s rate of advance. They are usually engrossed.
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