Homogeneous Catalysts

Catalysis in the stratosphere

One of the most serious environmental concerns we have today is the depletion of the ozone layer in the part of the upper atmosphere known as the stratosphere. A key feature of the ozone problem is a form of homogeneous catalysis where the reactants, products and catalyst are all gases.

The Earth's atmosphere is made up of a number of thin layers close to the surface of the Earth. The ionosphere goes up to about 550 km.


Formation and removal of ozone

The ozone layer is essential to life on Earth because it absorbs ultra violet radiation from the sun that would be very damaging to organisms like ourselves on the surface of the planet.

O3 + hn

O2 + O

Ozone loss

Ozone is also removed from the atmosphere by collision with oxygen atoms.

O3 + O


Ozone creation

These natural processes by which ozone is removed are balanced by the collision between dioxygen molecules and oxygen atoms that continually generates ozone in the atmosphere.

O2 + O


Ozone balance

There is, therefore, a natural balance between the formation and removal of ozone in the stratosphere that keeps the protective ozone layer intact. We call such a situation, where the rate of formation of ozone is equal to the rate of removal of ozone, a steady state.

Hole in the ozone layer

In 1985, scientists discovered that the ozone concentration in the stratosphere above Antarctica was much lower than expected. They had discovered a 'hole' in the ozone layer. The ozone was being removed faster than expected because of human activity.
Watch an animation.

The ozone layer. Blues represent less ozone.


Images courtesy of The Centre for Atmospheric Science.