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
Ontario electricity policy of carbon dioxide, 0.05 kg of sulfur dioxide and 0.8 kg of nitrogen oxides (NO) per megawatt-hour of energy generated. Compared with coal, natural gas generates about half as much carbon dioxide, one-third of the nitrogen oxides, and one one-hundredth of the sulfur oxides. Natural gas is most commonly used for heating applications in homes and businesses but natural gas-fired power generation is also a significant component of the power supply mix, accounting for 8% of Ontario's power generation capacity, with 102 natural gas generating stations. This capacity is set to increase from 5,103 MW to 9,300 MW by 2010.