Scientists decode the atmosphere's 'detergent'

A team from the University of Pennsylvania has identified an important intermediate molecule and tracked its transformation to hydroxyl radicals - highly reactive molecules that are known as the atmosphere's 'detergent'.

The study demonstrated the amount of energy necessary for the reaction to take place and also helped explain how the atmosphere maintains its reserves of hydroxyl radicals.

"Hydroxyl radicals are called the atmosphere's detergent because most pollutants that go into the air are broken down by them," explained Marsha Lester, professor of chemistry in University of Pennsylvania's school of arts and sciences.

Since they are so reactive, the question is how is it that there is so much of it in the atmosphere?

"We used a laser to generate a fingerprint of this intermediate molecule, based on the wavelengths of light it absorbs. The laser also supplies the energy necessary to drive the reaction, which would be provided by heat under atmospheric conditions," Lester noted.

Researchers noticed that a hydrogen atom from one end of the intermediate molecule transfers over and bonds to an oxygen atom on the other side.

The molecule then breaks apart, resulting in a hydroxyl radical.

The team believes that the new understanding of the amount of energy necessary to drive this hydrogen transfer reaction will have implications for many of the hydroxyl-radical-producing reactions that involve "Criegee intermediates".

In 1949, German chemist Rudolf Criegee hypothesized that alkenes, a class of chemicals with carbon double bonds, were broken down in reaction with ozone by way of intermediate molecules that were even more reactive and short-lived.

These intermediate molecules are now known as "Criegee intermediates".

"Earth's atmosphere is a complicated dance of molecules. The chemical output of plants, animals and human industry rise into the air and pair off in sequences of chemical reactions. Such processes help maintain the atmosphere's chemical balance; for example, some break down pollutants emitted from the burning of fossil fuels," researchers informed.

The study was published in the journal Science.