Acid Rain

15 Pages 3648 Words

ow Is Acid Rain Formed? Acid rain consists mainly of acids formed in the atmosphere. It consists of the oxides of sulfur, SO2 and SO3, and of nitrogen NO and NO2. Let us examine the major contributor to acid rain, sulfur oxides. Natural sources which emit sulfur dioxide include volcanoes, sea spray, plankton and rotting vegetation. Despite these natural occurrences, the burning of fossil fuels (such as coal and oil) can be largely blamed for the emissions. The chemical reactions begin as energy from sunlight, in the form of photons, hit ozone molecules (O3) to form free oxygen (O2), as well as single reactive oxygen atoms (O). The oxygen atoms react with water molecules (H2O), producing electrically charged, negative hydroxyl radicals (HO). These hydroxyl radicals are responsible for oxidizing sulfur dioxide and nitrogen dioxide, which produces sulfuric acid and nitric acid. Some particles will settle to the ground (in the form of acid deposition) or vegetation can absorb some of the SO2 gas directly from the atmosphere. When sulfur dioxide comes in contact with the atmosphere, it oxidizes and forms a sulfate ion. It becomes sulfuric acid as it joins with hydrogen atoms in the air and falls down to earth. Oxidation occurs most in clouds, especially in heavily polluted air, where other compounds such as ammonia and ozone help to catalyze the reaction, increasing the amount of sulfur dioxide changing to sulfuric acid. Not all of the sulfur dioxide is converted to sulfuric acid, and it is not uncommon for a substantial amount to float up into the atmosphere, move to another area, and return to earth as sulfur dioxide, unconverted. S (in fossil fuels) + O2 =* SO2 2 SO2 + O2 =* 2 SO3 Much of the sulfur dioxide is converted to sulfur trioxide in the atmosphere SO3 + H2O =* H2SO4 The sulfur trioxide can then dissolve within water to form sulfuric acid Nitric oxide and nitric dioxide are mainly from power plants and exhaust fumes. Similar to su...