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
Lower sulfur oxides Disulfur monoxide (SO) is an unstable analogue of sulfur dioxide. Like SO as well as ozone (O), and trisulfur (S), it adopts a bent structure. The S-S bond length is 188.4pm, the S-O bond is 146.5pm and the SSO angle is 117.88. The two dipole moment components are μa = 0.875D and μb = 1.18D This species decomposes to give a polymeric sulfur oxides ("PSO's") with the approximate formula [SO]. PSO's decompose at room temperature to elemental sulfur and SO. PSO's have been proposed to be responsible for the colour of Io. Trisulfur monoxide, SO is an unstable molecule. It