Atmospheric Chemistry

Portrait of Karena McKinney
Karena McKinney
Associate Professor of Chemistry

On a smoggy day, when it’s harder to see the skyline, we get a glimpse of something else: The complex story of our air.

From driving cars to spraying chemicals to making electricity, modern life sends a cocktail of gases into the atmosphere every day. We know that some of these gases are stoking climate change and pollution, but the details of how these compounds react with the natural world are still, well, hazy.

Associate Professor of Chemistry Karena McKinney, an atmospheric chemist who joined Colby’s faculty in 2017, studies those details. Specifically, she explores what happens when emissions from humans collide with those from trees and plants.

Standing forests play a critical role in socking away planet-warming carbon dioxide. But they also emit volatile organic compounds (VOCs), the same types of gases we try to minimize in paints, carpets, and other human-made products.

These plant-produce , or biogenic, VOCs, have always been a part of the natural cycle. What’s changed, McKinney said, is that in an industrialized world, “there can be interesting interactions between natural emissions and anthropogenic emissions that can actually shift the chemistry in ways that produce pollution.”

McKinney has demonstrated this effect in the Amazon by sampling rainforest air downwind of Manaus, a Brazilian city of about two million people. Like other urban areas, Manaus gives off nitrogen oxide, or NOx: “You get lots of it anytime you have a city with cars and power plants and lots of oxidation going on,” McKinney said.

“If we want to control air quality and address climate change, the solution won’t involve fiddling with nature’s emissions—it will be about cleaning up man-made ones.”

—Karena McKinney, associate professor of atmospheric chemistry

She and her fellow researchers have been able to demonstrate that when those human-caused NOx emissions meet the rainforest VOCs, they react with each other to produce more oxidants—namely ozone, she says, “which essentially means you’re making smog.”

To conduct their work, McKinney and other atmospheric researchers often measure the air from towers above the forest canopy or at “receptor sites” where emissions from people meet those from trees. Lately, though, McKinney has been experimenting with drones to get to territory that’s otherwise unreachable. She has designed and built an air sampler specifically to fly on a commercial drone. “That’s going to be a powerful new way of collecting samples,” she said.

She knew by her junior year at Harvard University that atmospheric chemistry would be her field. “I got excited about the idea that I could both do chemistry and do something that had this very tangible effect in terms of its benefit for society,” she said.

Sampling rainforest air downwind of Manaus, Brazil

The chemistry of our air involves a fine balance with many questions yet to be answered. How that balance tips in different scenarios is intricately tied to climate change, of course, but it also has implications for respiratory health and how we use land—even the kinds of trees we plant in city parks. It turns out that VOC emissions vary among species.

If we want to control air quality and address climate change, she emphasizes, the solution won’t involve fiddling with nature’s emissions—it will be about cleaning up man-made ones.

“We need to have a pretty detailed understanding of these underlying mechanisms,” McKinney said, “in order to be able to have effective policy.”

“Yes, the biogenic emissions contribute” to pollution, she said. “But that’s not the knob that you want to turn.”