What must the pH of water in the atmosphere be to create acid precipitation?

Acid precipitation, commonly known as acid rain, occurs when atmospheric water vapor combines with certain pollutants, such as sulfur dioxide and nitrogen oxides, leading to the formation of sulfuric and nitric acids. For precipitation to be classified as acid rain, the pH of the water must be significantly lower than that of pure water, which has a neutral pH of 7.

A pH of 5.6 or lower indicates that the water is acidic. This level is derived from the natural presence of carbon dioxide in the atmosphere, which forms carbonic acid when dissolved in water, resulting in a slightly acidic pH of around 5.6. Therefore, any precipitation with a pH below this threshold can be considered acid precipitation. Options that suggest a pH higher than 5.6 would not qualify as acid precipitation, as they would not meet the necessary acidity level associated with the formation of harmful environmental effects such as soil and waterway acidification.