Acid rain usually has a pH between 4.2 and 4.4. Normal rain has a pH of about 5.6 it is slightly acidic because carbon dioxide (CO 2) dissolves into it forming weak carbonic acid. The lower a substance's pH (less than 7), the more acidic it is the higher a substance's pH (greater than 7), the more alkaline it is. For example, in desert areas the ratio of dry to wet deposition is higher than an area that receives several inches of rain each year.Īcidity and alkalinity are measured using a pH scale for which 7.0 is neutral. The amount of acidity in the atmosphere that deposits to earth through dry deposition depends on the amount of rainfall an area receives. When the accumulated acids are washed off a surface by the next rain, this acidic water flows over and through the ground, and can harm plants and wildlife, such as insects and fish. The acidic particles and gases may deposit to surfaces (water bodies, vegetation, buildings) quickly or may react during atmospheric transport to form larger particles that can be harmful to human health. Dry DepositionĪcidic particles and gases can also deposit from the atmosphere in the absence of moisture as dry deposition. The sulfuric and nitric acids formed in the atmosphere fall to the ground mixed with rain, snow, fog, or hail. Wet deposition is what we most commonly think of as acid rain. Winds can blow SO 2 and NO X over long distances and across borders making acid rain a problem for everyone and not just those who live close to these sources. Manufacturing, oil refineries and other industries.Two thirds of SO 2 and one fourth of NO X in the atmosphere come from electric power generators.
These then mix with water and other materials before falling to the ground.
The SO 2 and NO X react with water, oxygen and other chemicals to form sulfuric and nitric acids. Acid rain results when sulfur dioxide (SO 2) and nitrogen oxides (NO X) are emitted into the atmosphere and transported by wind and air currents.