How is acid rain formed?

Question

How is acid rain formed?

Answer 1

Acid rain is caused by the release of the gases SO2 (sulphur dioxide) and NOX (nitrous oxides). The main sources of NOX emissions are vehicles and fuel combustion.

Sulphur dioxide reacts with water vapour and sunlight to form sulphuric acid. Likewise NOX form nitric acid in the air. These reactions takes hours, or even days, during which polluted air may move hundreds of kilometers. Thus acid rain can fall far from the source of pollution.

When mist or fog droplets condense they will remove pollutants from the air and can become more strongly acid than acid rain. Even snow can be acid. Gases and particles, not dissolved in water, with a low pH can also be deposited directly onto soil, grass and leaves. It is possible that even more acidity is deposited in this way than by rain. Not much is known about this process, and it is particularly difficult to study.

Answer 2

Acid rain in formed when precipitants: rain, snow, sleet, fog etc react with   emissions from mostly human activity, the most common being sulfur and  nitrogen. This reaction forms an acid and then falls to the ground in the previously mentioned forms.  

Answer 3

rain + chemical pollutants emitted from the factories...