A nacreous cloud glows in a sky that has already darkened. What is happening high above us?

Chemistry, behind the color. Nacreous clouds form at about 15 to 25 kilometers, far above most weather clouds. The sun still lights them after dark on the ground, and droplets or crystals of acid and ice scatter intense colors. The surfaces of those particles act as a surface for chemical reaction and convert stable chlorine compounds into forms able to destroy ozone when the spring light returns.

Nacreous clouds form at about fifteen to twenty-five kilometers, far above most weather clouds, and require extreme cold.

Up there the sun still shines after dark on the ground, and the acid and ice crystals are small and uniform, so they scatter the light into intense colors against a dark sky.

The part you cannot see matters more. In a thin gas molecules rarely meet, and on the faces of the particles they stick and react, so the cloud works as a surface for chemical reaction.

There stable chlorine compounds, which come from human-made pollutants, are converted into forms that wait for light and destroy ozone with the polar spring sunrise. That is how the beauty ties to the chemistry of the polar hole. No nacreous cloud causes ozone loss by itself: chlorine, sustained cold and sunlight are needed too.