What is the health hazard is shown in this picture?

The purple-blue in this picture is the hole in the ozone layer over Antarctica The picture  is generated by a Total Ozone Mapping Spectrometer (TOMS) carried in a satellite (see Centre for Atmospheric Science University of Cambridge http://www.atm.ch.cam.ac.uk/tour/part2.html )

The ozone layer protects terrestrial life from injury by solar ultraviolet radiation.  Individuals living in regions with reduced ozone protection, for example Argentina and Australia have an increased incidence of skin cancer

Between 1975 and 1994, the  ozone in measured over Antarctica  was reduced to less than half its value during the 1970s, This dramatic fall in ozone was caused by the use of man-made chemicals known as halocarbons which include the well-known CFCs commonly used in fridges and so on. These CFCs had made their way into the upper atmosphere where the much stronger UV radiation from the sun had broken them down into their component molecules, releasing the potentially damaging chlorine (and bromine) atoms, which, given the right conditions, could destroy ozone.

To limit further damage to the ozone layer in the stratosphere the Montreal Protocol was signed in 1987 by many countries to greatly reduce the production and use of CFCs which had been shown to be responsible for damage to the ozone layer. Since 1987, further amendments to the protocol have imposed even greater restrictions of the production and use of potentially damaging compounds. It may be more than a century before the ozone layer returns to normal.