Acid rain

Acid rain was unnaturally acidic rain.

Skaro, and especially Kaalann, had become so polluted that it constantly rained acid. (GAME: City of the Daleks)

Marran Alpha had constant acid rain. (AUDIO: The Dark Flame)

In 5345, the Harvest Rangers used satellites to produce acid rain to melt down Androzani trees for fuel. (TV: The Doctor, the Widow and the Wardrobe)