Cleanest Air in the World Discovered

Scientists have discovered Earth's cleanest air, finding an atmospheric region unaffected by human activities. The area, over the Southern Ocean, between the south of Australia and Antarctica, was found to be free from anthropogenic aerosols, making it "truly pristine," scientists say.

The atmosphere is hugely diverse in terms of what it is made up of. Aerosols are fine solid particles or liquid droplets in the air that can be manmade or natural. They can influence climate and weather patterns because they reflect the sun's energy back into space. But their distribution is not uniform, so understanding how and where they travel is important.

Researchers from Colorado State University and the Australian Bureau of Meteorology carried out a profile of bacteria in the boundary layer of air that feeds clouds in the lower atmosphere. Previous research has suggested the air above the Southern Ocean would be one of the areas least affected by human influence, but there had been no region-wide assessment of bioaerosols and their sources.

"Climate models have historically struggled to represent clouds and energy transfer in the Southern Ocean, typically making the clouds too 'icy' and not possessing the liquid water that is seen by satellites to persist at the tops of clouds," the team told Newsweek in an email. "Too much sunlight was making it to the surface in the models. One possible reason is that the aerosols feeding clouds over the Southern Ocean are remarkably and consistently different than elsewhere on Earth, due to their isolation from aerosols released from large land masses. This information is not considered in most climate models, and there have been few observational studies of clouds and aerosols in this region."

They said the potential that these clouds are being controlled by an "unusually pristine atmosphere" made them want to understand the particles themselves.

The team took samples of ambient aerosols between the altitudes of 42.8 to 66.5 degrees south during a research voyage. Their findings, published in the journal PNAS, show what is in the air above the Southern Ocean and where it came from. They looked at the bacteria in the samples and used this as a "diagnostic tool" for understanding the air above, study co-author Thomas Hill, from Colorado State University, said in a statement.

"For example, that the aerosols controlling the properties of Southern Ocean clouds are strongly linked to ocean biological processes, and that Antarctica appears to be isolated from southward dispersal of microorganisms and nutrient deposition from southern continents," he said. "Overall, it suggests that the Southern Ocean is one of very few places on Earth that has been minimally affected by anthropogenic activities."

Microorganisms can be transported thousands of miles on the wind, meaning particles produced in one part of the world can impact the atmosphere in far away regions. Analysis of the Southern Ocean samples showed that most of the microorganisms came from the ocean. At different latitudes, bacterial composition differed, getting less diverse the closer it got to Antarctica. This, scientists say, suggests the Southern Ocean is largely isolated from anthropogenic particles produced in other parts of the world.

They told Newsweek that they were slightly surprised even samples from just below Tasmania were dominated by marine bacteria.

"A consequence and implication for this region's marine boundary layer and the clouds that overtop it is that it is truly pristine, free from continental and anthropogenic influences," the team wrote. They said that while the study was limited because samples were only taken from one longitudinal range. However, they said the findings support the idea that the Southern Ocean is one of the few areas on Earth "that is unlikely to have changed due to anthropogenic activities."

The researchers now hope to look at seasonal and annual cycles of aerosols in the region. They will also be heading north to the Arctic to investigate how biologically-mediated particles may be affecting cloud properties—something that is currently not well understood.

This article has been updated to include more quotes and information from the researchers.

southern ocean
Aerosol filter samplers probe the air over the Southern Ocean. Researchers say the air sampled is the unaffected by human activities. Kathryn Moore