When light levels are low, the pupil will become to allow more light to enter the eye?

Dilated. As the amount of light decreases, the iris dilator muscle is constricted whilst the iris sphincter muscle relaxes. This increases the amount of light that can enter the eye, allowing you to see better in lower light conditions. The opposite effect occurs when light levels increase.

My best guess would be: The amount of acid in rain, the amount of ground level ozone, and the amount of particulate matter. I'm not 100% on this one, sorry! <3