* They are not easily broken down: CFCs are very stable molecules, meaning they don't readily react with other substances in the lower atmosphere. They resist decomposition by sunlight, water, or other atmospheric components.

* They are not soluble in water: Unlike many other pollutants, CFCs don't dissolve in water droplets, so they don't get washed out of the atmosphere by rain.

* They are lighter than air: CFCs are less dense than air, which means they tend to rise into the upper atmosphere.

However, their stability is what makes them harmful in the stratosphere:

* Ultraviolet radiation: When CFCs reach the stratosphere, they are exposed to high levels of ultraviolet (UV) radiation from the sun. This radiation breaks down the CFC molecules, releasing chlorine atoms.

* Ozone destruction: These chlorine atoms act as catalysts in a chain reaction that destroys ozone molecules, which are essential for protecting life on Earth from harmful UV radiation.

So, while CFCs are relatively harmless in the lower atmosphere, their stability allows them to migrate to the stratosphere, where they cause significant damage to the ozone layer.