Growing up on a farm near the rural town of Brooklyn, in northwestern Pennsylvania, Kerri Pratt didn’t even know what the initials “Ph.D.” stood for. Today, Pratt, 30, not only holds a Ph.D. in atmospheric chemistry from the University of California, San Diego, she’s a working scientist, supported by a postdoctoral fellowship. Since February, Pratt has been stationed in Barrow, Alaska, the northernmost town in America, working with a team of scientists who are studying how the ocean and the atmosphere interact with each other, how pollutants play into those interactions, and how climate change is affecting the entire system.
It might seem a little dry and technical, to say nothing of cold, but Pratt is having the time of her life. “Normally, it’s minus 30,” she said in a satellite-phone conversation, “with a wind chill of minus 50. But today it’s warm — minus 20, with no wind. There isn’t a cloud in the sky. It’s just beautiful. This is a dream come true for me.”
Pratt has been dreaming of the far north since she was a child. “My Ph.D. advisor would tell me, ‘most students want to head south, go somewhere they can surf, do research in the Maldives,’” Pratt said. “I was the one begging to go to the Arctic.” When her postdoctoral advisor told her about the NASA BROMEX project, she knew she wanted to be involved. The acronym stands for “Bromine, Ozone, and Mercury Experiment,” and it’s based on the fact that naturally occurring salts containing bromine evaporate from the ocean surface, and mix with the overlying air. (The same happens with chlorine; both elements, along with fluorine and several others, are known collectively as halogens.)
In the Arctic, there’s almost always snow on the ground and atop sea ice during winter and spring, so this chemically enhanced air flows over snow crystals — and when it does so, the bromine and chlorine react with and destroy atmospheric ozone. In the stratosphere over the Antarctic, manmade chlorine flows over ice crystals to destroy high-altitude ozone, causing the infamous ozone hole, but in the Arctic, low-level ozone destruction is largely natural.
Credit: Kerri Pratt
One big question BROMEX is trying to answer is how the changes in sea ice due to global warming are affecting this process. As the Arctic Ocean melts back more every summer (on average), older, multi-year ice is being replaced over the winter with thinner, saltier, halogen-rich first-year ice. “One reason we’re up here now,” Pratt said, “is that this is the season when we go from dark to light, and it's also the time when the sea ice breaks up.”
They can, in other words, watch the ocean-atmosphere interaction under a variety of conditions, to understand the process better. For example, Pratt said, a lead opened up recently in the ice — a long, narrow patch of open water, which then refroze. She and her advisor, Purdue scientist Paul Shepson, flew over the lead in his small, instrument-laden plane, taking readings in both situations to see how the air was changing. The team also uses satellite data, as well as measurements from buoys and on the tundra. They even do experiments in a “snow chamber” (“It’s a fancy way of saying ‘a box we put snow in,’ Pratt said), where they pass various gases across the snow in a controlled fashion to try and characterize the chemical reactions in detail.
Mercury, the third substance in the BROMEX acronym, is the most troubling. This toxic metal, spewed into the air in the exhaust of coal-fired power plants and in other industrial processes, makes its way to the Arctic. Once there, it reacts with the halogens and gets deposited onto the tundra. From there, it makes its way into the food chain, and ultimately into the animals eaten by members of the of the native Inupiat community. Winds also carry volatile organic pollutants northward. “They’re ordinarily not reactive with atmospheric oxidants, but the they can react with the halogens,” Pratt said. Like mercury, they end up deposited on the ground.
Credit: Kerri Pratt
Mercury and other toxins are affecting polar bears as well, but while humans are threatening the magnificent white predators collectively, members of the BROMEX team could be attacked any time they go out onto the ice to take a reading. “We haven’t run into one yet,” Pratt said, “which is a good thing. They can outrun a snow machine. Any time we go out on the ice, a bear guard with a gun has to go with us and stand on the highest point to keep watch.” Shooting a polar bear would be a last resort, however, she hastened to add. Most of the time they're scared away by the sound of a snow machine.
Trying to understand the interactions of ocean, air, ice and pollutants is a complicated task, and there aren’t any clear answers yet. But Pratt loves the challenge of trying to figure it all out. “We’ve had great luck so far,” she said. She also loves being in the Arctic. “We met with the local whaling captains,” she said, to ask for permission to do research in their hunting areas; the leads where the scientists look for bromine in the air are also where bowhead whales come up to breathe. “One of the captains invited us to his house, and told us all about traditional subsistence whaling. I’ve been blessed with an amazing experience,” she said. “I really hope I can keep doing Arctic research for many years to come.”
You can follow Pratt’s blog, and see a lot more photos, here.