The stratosphere is a layer of gas that starts somewhere between 12.9km (over the Poles) and 19.3 km (over the Equator) above the surface of the Earth, depending on where you are and ends almost 50km above us! The stratosphere has virtually no clouds or weather. When oxygen molecules (O2) reach the stratosphere and are hit by strong ultraviolet rays from the sun’s they can split up into two separate oxygen atoms (O2 + UV = O + O). If one of these joins on to an oxygen molecule, it forms an ozone molecule, which is O3 (O2 + O = O3).
At lower levels in the atmosphere ozone acts as a greenhouse gas helping trap heat and so contributes to global warming. At ground level it is a poisonous gas and can cause health problems such as asthma and bronchitis. It is formed by the action of sunlight on carbon based chemicals (volatile organic compounds) when they are combined with a group of pollutants called nitrogen oxides.
But ozone isn't just about the stratosphere. Although in the stratosphere is where we want ozone to be. Ground-level ozone, or tropospheric ozone, emitted by the burning of fossil fuels in power plants and through car emissions lead to increased rates of asthma and heart disease. In November 2014 the American government began the consideration of updating their 2008 standard on ground-level ozone to restrict and reduce emissions. Though proposed standards and methods are quoted to become "the most expensive regulation of all time", according to this report by the National Geographic Society. Can we put a price on clean air and healthy people?
Learn more about the science of ozone on NASA's OzoneWatch website.
Now let's take a look at how the ozone layer is changing.