THE cleanest air on Earth has been found — in the middle of Antarctica’s Southern Ocean.
Scientists pinpointed the pristine ‘atmospheric region’ which remains unaffected by humans.
The study, the first to measure its air quality, found no traces of particles from human activity or transported from far afield.
Study co-author Dr Thomas Hill, of Colorado State University in the US, said: ‘We were able to use the bacteria in the air over the Southern Ocean as a diagnostic tool to infer key properties of the lower atmosphere.
‘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.’
Dr Hill added ‘Overall, it suggests the Southern Ocean is one of very few places on Earth that has been minimally affected by anthropogenic [man-made] activities.’
Pollutants such as aerosols are spread around the world by complex climate and weather processes, making it difficult for scientists to find places that have not been contaminated by human activity.
The team used a marine research vessel to collect air samples from lower parts of the atmosphere, the marine boundary layer which comes into direct contact with the ocean.
The air samples were analysed for ‘airborne microbes’, which are spread by winds throughout the atmosphere over hundreds of thousands of kilometres.
Using DNA sequencing, source tracking and wind trajectories, the team were able to establish the microbes had come from the ocean rather than other parts of the globe.
Dr Hill said: ‘A consequence and implication for this region’s marine boundary layer and the clouds that overtop it are that it is truly pristine, free from continental and anthropogenic influences, with the ocean as the dominant source controlling low-level concentrations of cloud condensation nuclei and ice nucleating particles.
‘The researchers, at every stage, treated the samples as precious items, taking exceptional care and using the cleanest technique to prevent contamination from bacterial DNA in the lab and reagents.’
Dr Hill said that they found no trace of aerosols, suggesting pollution from human activity was not travelling south into Antarctic air.
The air was so pure that they had very little DNA to work with.
The findings, published in Proceedings of the National Academy of Sciences, challenge previous research which assumed most airborne microbes in the region came from upwind continents.