The basics of Ozone depletion

This blog will briefly outline the factors involved ozone depletion. The video in the previous post explains very succinctly the processes, please give the video a watch as it will add great visual demonstration to my basic definitions below.

proteckllc.com

Firstly, Chlorofluorocarbons (CFCs), manufactured in refrigeration, air conditioning, aerosols and solvents, contain chlorine compounds. Chlorine is then released in the stratosphere due to a photolytic reaction (breaking up of particles by photons in light waves) with incoming UV rays. In turn, the release of chlorine into the ozone rich layer of the stratosphere initiates a catalytic (chlorine is not destroyed) reaction:

CI + O3 -> CIO + O2, CIO + O -> CI + O2

This reaction depletes ozone leaving chlorine and oxygen present. Rowland & Molina first suggested this reaction in 1975, but it was not until the ozone “hole” was first detected in 1985 that any measures were put in place to limit the production of CFCs. These measures were directed through the Montreal Protocol, which will be discussed in more detail on a future blog.

jpl.nasa.gov

Polar Stratospheric Clouds (PSCs) form in extremely cold temperatures (about -80 degrees Celsius) during winter from aggregations of water vapour and nitric acid. PSCs were discovered to be the surface upon which Chlorine was converted to its most reactive (and ozone depleting) form, causing the above photolytic and catalytic reactions to be enhanced when sunlight reaches the poles in springtime.

The influence of the Polar Vortex (as discussed in detail by Schoeberl and Hartmann 1991) on ozone depletion is through the indirect effect of providing and sustaining the conditions necessary for PSC formation and existence till springtime. The vortex is a cyclone generated by the steep temperature gradient between high and mid-latitudes present especially during winter, combined with the earths rotation. This steep gradient described as the polar front fluctuates according to many factors including incoming solar radiation and rossby wave strength which determine the scale of the Polar Vortex. When it is especially strong (for example Arctic winter 2011) the PSCs are present much later into spring and therefore more ozone depletion occurs.

It is important to consider that these factors combine to rapidly enhance ozone depletion at the poles. I have only covered the factors briefly, but these processes provide the basis for the creation of the ozone hole and will be refered to in my blog when I introduce case studies of how the past, present and future ozone levels are measured.