Revealed: The mystery behind earth’s cleanest air

Clouds and rain play a key role in scrubbing the air clean above the Southern Ocean, scientists say

Rain and clouds play a key role in making the air above the Southern Ocean the cleanest on the planet, scientists have found.

Although this ocean in the Antarctic region has less human activity, it is still made unclean by aerosols from natural sources such as salt from the sea, dust from winds, or particles from tiny plant-like organisms called phytoplankton.

But clouds and rain play a key role in scrubbing the atmosphere above the Antarctic ocean clean, researchers said.

The scientists used data from a new generation of satellites to develop a computer programme to recognise different cloud patterns over vast areas of this ocean.

They looked in particular for distinctive honeycomb-shaped patterns in the clouds known to play a major role in regulating the climate.

The honeycomb cells in these special clouds are either in an “open” or “closed” state, relating to the amount of rainfall the region they cover gets.

The scientists compared data from the honeycomb cloud pattern analysis with aerosol measurements from the Cape Grim observatory in Tasmania, and also with the Bureau of Meteorology’s rainfall observations.

They found that the days with the cleanest air were associated with open honeycomb clouds, which scientists suspect generate sporadic but intense rain showers that could “wash” aerosol particles out of the air.

In the open state, these clouds appear to hold more moisture and produce more rain than the fluffy white closed clouds.

“We found the open honeycomb clouds produce six times as much rain as the closed ones,” the scientists wrote in The Conversation.

“We found the empty honeycombs to be far more common during the winter months, when the air is cleanest,” they added.

The researchers said these honeycomb patterns were also found in the North Atlantic and North Pacific regions during winter.

In further research, they hope to explain how the clouds in these regions remove aerosols including dust and pollution.