First, due to the extensive use of fossil fuels such as coal, oil and natural gas, sulfur oxides or nitrogen oxides produced after combustion undergo complex chemical reactions in the atmosphere, forming sulfuric acid or nitric acid aerosols, or being captured and absorbed by clouds, rain, snow and fog, and falling to the ground to become acid rain.

Second, these three areas have a suitable climate and a lot of precipitation (so they become densely populated areas), which is a necessary condition for serious acid rain harm.