the.com/acid rain

means Rain, snow, or fog made acidic when sulfur dioxide and nitrogen oxides from burning fossil fuels mix with atmospheric moisture.

from A plainly descriptive term, not a poetic one — coined in the 1800s by a Scottish chemist studying industrial pollution over Manchester, who noticed rainfall near factories was corroding stone and vegetation and simply named what he found. The phrase waited in obscurity for a century before it resurfaced in the mid-1900s as scientists connected coal smoke, car exhaust, and dying forests across whole regions, turning a lab observation into one of the first household phrases of environmental alarm.