The molecule's existence was predicted over 20 years -- now scientists are discovering how it 'burns up' or oxidises pollutants, such as nitrogen compounds from factories and cars.

Pollutants that aren't processed then fall back to earth in the form of acid rain.

"The chemical details of how the atmosphere removes nitric acid have not been clear," said Professor Joseph Francisco of Purdue University.

"This gives us important insights into this process."

"Without that knowledge we really can't understand the conditions under which nitric acid is removed from the atmosphere."

"This becomes important in emerging industrial nations such as China, India and Brazil where there are automobiles and factories that are unregulated."

"This chemistry will give us insight into the extent that acid rain will be a future concern."

The newly discovered molecule has two hydrogen bonds, which allows it to form a six-sided ring structure.

Hydrogen bonds are normally weaker than other bonds between the atoms in a molecule, known as covalent bonds.

Covalent bonds are 20 times stronger than hydrogen bonds -- yet these two hydrogen bonds are strong enough to affect the atmosphere.

"We've speculated about this unusual atmospheric species for many years, and then to actually see it and learn about its properties was very exciting," said Professor Marsha Lester of the University of Pennsylvania.

"The reaction involving this molecule proceeds faster as you go to lower temperatures, which is the opposite of most chemical reactions."

"The rate of reaction also changes depending on the atmospheric pressure, and most reactions don't depend on external pressure."

"The molecule also exhibits unusual quantum properties."

Professor Lester pointed out that it was these unusual properties that left the molecule undiscovered for so long.

"This is not how we explain chemistry to high school students," she said.