The correct answer is option 4: Poles.

Ozone holes are areas in the ozone layer where the concentration of ozone is significantly depleted. These holes are more pronounced at the poles, specifically the North Pole and the South Pole.

There are a few reasons why ozone holes are more pronounced at the poles. Firstly, the temperature at the poles is much colder compared to other regions. Cold temperatures enhance certain chemical reactions that lead to the destruction of ozone molecules, causing the formation of ozone holes.

Secondly, polar regions experience a meteorological phenomenon called polar vortex. The polar vortex is a large-scale circulation of air that isolates the polar region from warmer air in other parts of the atmosphere. This isolation traps the cold air in the polar regions, leading to even lower temperatures and further supporting the formation of ozone holes.

It is important to note that while ozone depletion occurs globally to some extent, the most severe depletion and the formation of large ozone holes are observed at the poles.