Why is airborne and water borne chemicals both local and global issues

Air and water borne chemicals are both local and global issues because of the potential hazard they may pose to human life and their ability to travel and affect more than one countries or regions.
One such example is the growth of the ozone layer in the 1980s over Antarctica. CFC used globally became concentrated at the south pole and caused the depletion of the layer. The hole appeared in Antarctica even though there are no industries or even individuals there to emit these gases.