The naturally pristine atmosphere above Antarctica nevertheless contains black carbon, a heat-trapping air pollutant, and a new study found that it is largely produced by vegetative fires of both natural and human causes in South America, Africa and Oceania.

By running an air-quality model for the Southern Hemisphere, a research team led by Chilean scientists found that the fires accounted for 20% to 50% of Antarctica's atmospheric black carbon. Though the pollutant is at only low concentrations in the South Pole's air, a worsening of fires could accelerate melting and other climate disruptions, according to their paper published March 10 in Science of The Total Environment.

A major component of soot, black carbon is created when plants and fossil fuels are burned, both during wildfires and when it is used by humans for fuel or to clear land. Because of their dark color, the microscopic particles absorb heat and contribute to global warming. Black carbon can also cover snow and limit its ability to prevent warming by reflecting sunlight back out of the atmosphere, lowering its albedo.

Although black carbon is a well-known pollutant that also causes cardiovascular and respiratory diseases, data on its prevalence in Antarctica is relatively sparse. Study author Ernesto Pino-Cortés, an academic researching air quality at the Pontifical Catholic University of Valparaíso, said his group found "just a few studies" measuring black carbon on the icy continent.

According to Pino-Cortés, the paper was inspired in 2014 when University of Tennessee Knoxville professor Joshua Fu shared research he had conducted that modeled the movement of black carbon in the Northern Hemisphere. The work of Fu, now a coauthor of the paper, encouraged the researchers to investigate the sources and transportation of the pollutant on the other half of the globe.

"Until our study, monitoring campaigns reported local and external sources, but most of them considered the analysis in a limited zone," Pino-Cortés said. "Our study analyzed the entire Antarctica region and estimated how anthropogenic and biomass burning emissions are transported during some of the Austral summer periods."

Pino-Cortés and his coauthors focused on the effects of biomass burning, which includes all burning plants other than residential burning of wood. Though Australia's devastating, record-breaking bushfires in 2019 and 2020 are perhaps the hemisphere's most infamous source of biomass burning, the scientists used data collected in 2014, when they measured daily black carbon concentrations at 15 locations throughout Antarctica.

In addition to emissions data for Southern Hemispheric countries, these emissions were entered into a model to simulate the levels of black carbon above Antarctica from January to April, when fires are most active in the area. A similar simulation erased biomass burning-related emissions to determine its impact.

Comparing the two simulations, the researchers found that Antarctica's atmospheric concentrations of black carbon would be 20% to 50% lower if all biomass burning in the Southern Hemisphere stopped. Their findings demonstrate the importance of wildfires and human-caused fires in creating pollution over the South Pole.

In the model, it took between 17 and 24 days for the Antarctic levels of black carbon to dip after the fires were "turned off," suggesting the length of time it takes for the pollutant to travel to the southernmost continent. The largest impacts occurred in the parts of Antarctica near Australia and New Zealand, where wildfires appear to be significant sources of black carbon.

Despite its climate-disrupting effects, black carbon has a lifespan of only a few weeks and is not currently building up in Antarctica, according to the authors.

"The good news," Pino-Cortés said, is that black carbon's concentration in the Antarctic air is less than 4 nanograms per cubic meter, "which is very low compared to the scenario in the North Hemisphere."

But intensifying fires that cause a buildup of black carbon, the authors said, "could consequently impact on the acceleration in the melting of snow and ice, the change in the albedo of this area of the cryosphere and significantly affect the Earth's radiative balance, aggravating the global climate change."

The research did not take into account emissions from scientific monitoring stations when creating their model, and it was also limited by some incomplete data on black carbon emissions in the Southern Hemisphere.

Pino-Cortés said his team is now expanding its research into Antarctic black carbon, including similar analyses during other years and the inclusion of other emission sources related to research and tourism in the area. Their investigations also include other light-absorbing particles such as brown carbon, which is often emitted alongside black carbon during fires.

The study, "The black carbon dispersion in the Southern Hemisphere and its transport and fate to Antarctica, an Anthropocene evidence for climate change policies," published March 10 in Science of The Total Environment, was authored by Ernesto Pino-Cortés and Samuel Carrasco, Pontifical Catholic University of Valparaíso; Luis Díaz-Robles, Francisco Cubillos and Roberto Santander, University of Santiago, Chile; Francisco Cereceda-Balic, Federico Santa María Technical University; Joshua Fu, University of Tennessee and Oak Ridge National Laboratory; and Jonathan Acosta, Pontifical Catholic University of Chile.