Internal combustion engine the atmosphere by the reaction of and volatile organic compounds in the presence of sunlight. Ground-level ozone is harmful to human health and the environment. Though the same chemical substance, ground-level ozone should not be confused with stratospheric ozone, or the ozone layer, which protects the earth from harmful ultraviolet rays. Carbon fuels contain sulfur and impurities that eventually produce sulfur monoxides (SO) and sulfur dioxide (SO) in the exhaust, which promotes acid rain. In the United States, nitrogen oxides, PM, carbon monoxide, sulphur dioxide, and ozone, are regulated as criteria air pollutants under the Clean Air Act to levels
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.