Air pollution alters the atmosphere in the remote Arctic

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Air pollution from fossil fuel burning reaches the remote Arctic in amounts large enough to alter its atmospheric chemistry, according to a study from Dartmouth College.

The findings highlight the far-reaching effects of fossil fuel emissions and emphasize the importance of clean-air regulations, which, the study shows, can reverse these effects.

The research points out that the impact of pollution on the Arctic began as soon as the industrial era saw widespread fossil fuel use.

The team discovered this pollution footprint in an unexpected place. The experts measured declines in methanesulfonic acid (MSA), an airborne byproduct of marine phytoplankton activity, which was trapped in Arctic ice cores when fossil fuel-related air pollution increased.

Levels of methanesulfonic acid Phytoplankton are vital to ocean food webs and carbon cycles, and methanesulfonic acid has been used as an indicator of their productivity. A drop in MSA is often interpreted as a sign of an ocean ecosystem in decline.

However, the Dartmouth-led team found that methanesulfonic acid levels also plummet in environments with high emissions from fossil fuel combustion, even if phytoplankton populations remain stable.

The models showed that air pollution causes dimethyl sulfide – initially produced by phytoplankton – to transform into sulfate instead of methanesulfonic acid, leading to a misleading decline in MSA levels.

Arctic pollution from distant sources The researchers observed sharp drops in MSA levels coinciding with the onset of industrialization. As Europe and North America began to burn large amounts of fossil fuels in the mid-1800s, MSA levels in Greenland ice cores began to fall.

Similarly, nearly a century later, MSA levels in Alaskan ice cores plummeted when East Asia experienced large-scale industrialization.

Study first author Jacob Chalif is a graduate student in the lab of senior author Erich Osterberg, an associate professor of earth sciences at Dartmouth.

“Our study is a stark example of how air pollution can substantially alter atmospheric chemistry thousands of miles away. The pollution emitted in Asia or Europe was not contained there,” said Chalif.

“By releasing all this pollution into the world, we’re fundamentally altering atmospheric processes. The fact that these remote areas of the Arctic see these undeniable human imprints shows that there’s literally no corner of this planet we haven’t touched.”

A millennium’s worth of climate data This study resolves a longstanding marine mystery related to the significance of MSA, said Osterberg, who led the extraction of a 700-foot ice core from Denali National Park.

Osterberg and his colleagues, including professors Cameron Wake at the University of New England and Karl Kreutz at the University of Maine, as well as Dartmouth alumnus Dominic Winski, had collected the core in 2013.

The ice core contained a millennium’s worth of climate data, including gas bubbles, particulates, and compounds like MSA.

“For centuries, MSA in the Denali core underwent minor fluctuations – until the mid-20th century when it falls off a table,” said Osterberg.

Mysterious change in atmospheric chemistry Initially, researchers suspected that the decline in MSA levels indicated a collapse in marine phytoplankton productivity. However, nothing fit the expected patterns.

Chalif and co-author Ursula Jongebloed, a Dartmouth alumna, connected while discussing these anomalies at a conference in 2022.

“We rethought all of our prior assumptions,” Chalif explained. “We knew that the declining MSA at Denali wasn’t due to marine productivity, so we knew some kind of change in atmospheric chemistry must be involved.”

Nitrate pollution in the Arctic The investigation eventually pointed to nitrate pollution, commonly emitted from burning fossil fuels, as the key factor.

“Pretty much to the year, when MSA declines at Denali, nitrate skyrockets. A very similar thing happened in Greenland,” Chalif said.

“At Denali, MSA is relatively flat for 500 years, no notable trend. Then in 1962 it plummets. Nitrate was similar, but in the opposite direction – it’s basically flat for centuries then it spikes upward. When I saw that I had a eureka moment.”

The research demonstrated that air pollution from fossil fuel combustion disperses across the Atlantic and Pacific Oceans, inhibiting the production of MSA in the Arctic.

This rules out the idea of a widespread marine ecosystem collapse as the cause of the MSA decline, and instead shows that pollution plays a direct role in preventing MSA formation.

Understanding the impacts of air pollution The findings open new possibilities for using MSA levels as a measure of atmospheric pollution, particularly in regions with no obvious emission sources.

“Marine ecosystem collapse just wasn’t working as an explanation for these MSA declines, and these young scientists figured out what was really going on,” Osterberg said.

“For me, it’s a new way of understanding how pollution affects our atmosphere. The good news is that we are not seeing the collapse of marine ecosystems we thought we were. The bad news is that air pollution is causing this.”

The power of air quality regulations However, the study also provided some hopeful news. Data from the Greenland ice core showed that when European and American air pollution became regulated, local atmospheric conditions began to stabilize.

MSA levels started to recover in the 1990s as nitrogen pollution decreased. Unlike carbon dioxide, which persists in the atmosphere for centuries, nitrogen oxides – the pollutants affecting MSA – dissipate within days.

“These data show the power of regulations to reduce air pollution, that they can have an immediate effect once you turn off the spigot,” said Osterberg.

“I worry about younger people resigning to an environmental crisis because all we hear about is bad news. I think it’s important to acknowledge good news when we get it. Here, we see that regulations can work.”

The research is published in the journal Nature Geoscience.

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