Weathering release occurs of Ca and other ions into surface waters. Rainfall is acidic because atmospheric carbon dioxide dissolves in the rainwater producing weak carbonic acid. In unpolluted environments, the rainfall pH is around 5.6. Acid rain occurs when gases such as sulfur dioxide and nitrogen oxides are present in the atmosphere. These oxides react in the rain water to produce stronger acids and can lower the pH to 4.5 or even 3.0. Sulfur dioxide, SO, comes from volcanic eruptions or from fossil fuels, can become sulfuric acid within rainwater, which can cause solution weathering to the rocks on which it
Nitrogen dioxide poisoning which nitrogen dioxide constitute one of the pollutants. While over 50% of the disease that results from these pollutants are common in developing countries and the effects in developed countries is also significant. An EPA survey in the U.S. suggests that 16 percent of United State's housing units are sited close to an airport, highway or railroad increasing in the United States the exposure risk of approximately 48 million people. A feasibility study of the ozone formed from the oxidation of nitrogen dioxide in ambient air reported by the WHO suggested that daily deaths of 1 to 2% is attributed