Question

Why do holes in the ozone layer happen to be located closer to the poles?

Answer 1

number of processes and effects that occur simultaneously are believed to be causing seasonal polar ozone depletion known commonly as the "Ozone Hole". These include:

the natural chemical reactions responsible for the production and destruction of ozone in the stratosphere (middle atmosphere)
the seasonal variations in incident sunlight on the planet
"special" features of polar weather that isolates this region of the atmosphere from the rest of the planet during part of the year
the addition to the atmosphere of ozone depleting chemicals through human activities
the pressence of "active surfaces" in the polar statosphere upon which ozone destruction reactions can be enhanced. This includes volcanic aerosols and polar stratospheric clouds.

To understand its distribution in the atmosphere, you must first know what ozone is and how it is naturally created/destroyed. Ozone is a molecule composed of 3 atoms of oxygen (O3). The "normal" oxygen we breath has 2 atoms of oxygen in it (O2). Ozone is constantly produced and destroyed by chemical reactions in the upper atmosphere that involve the breaking of O2 into two O atoms that then react with more O2 to make O3. Oxygen atoms are a type of "free radical", which is an atom or molecule with a very reactive electron on it. Light of ultra-violet wavelengths (around 300 nm) exites O2 and O3 molecules to the proper energy to allow both production and destruction reactions of O2 and O3 to proceed. These reactions normally absorb much of the UV radiation the sun directs towards us, protecting the Earth's surface from its harmful effects. The ozone reaction is actually more complex then the way I've just described it for two reasons: 1) it requires mediator molecules that help the reactions along by transferring some of the energy between the reacting molecules and 2) other chemical species can get involved, including other "free radicals" such as Cl and NO.
Ozone can be found in a number of locations in the atmosphere but here I restrict the discussion to statospheric ozone. Nature set up a balance for the production and destruction of ozone in the stratosphere by making available all the materials involved in the chemical reactions and keeping their concentrations relatively constant with time. One natural phenomenon that can disrupt this balance is a volcanic eruption that sends gasses and volcanic ash into the stratosphere. Not all eruptions do this but particularly violent ones (such as Mt. Pinatubo) can add particles to the upper atmosphere that will affect the ozone budget for some period of time.

Answer 2

Answer:

The main reason for ozone hole is CFCs . Chlorine atom from CFCs are responsible for converting ozone into dioxygen .At high temperature the chlorine atom react with nitrogen dioxide to form chlorine sink but at low temperature this reaction is not possible .

Now the CFCs released in the environment is spread all over the globe ( because it is hot and light )

and the temperature at poles is low hence the chlorine is available in atomic form ( because it can not form chlorine sink at low temperature ). This atomic chlorine causes holes in the ozone