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
Barbara J. Finlayson-Pitts from the reactions that occur within each layer. In the atmosphere, emitted gases and particles may react further to form new chemical species. Some compounds may not react within the troposphere, but will break down and participate in further transformations in the higher stratosphere. The inorganic chemistry of oxides of nitrogen and sulfur in the gas phase are better understood than the interactions of nitrogen and sulfur oxides with organic compounds. Finlayson-Pitts and her colleagues have done important work on understanding the chemistry of the troposphere, in particular, the conversion of nitric oxide (NO) to nitrogen dioxide (NO2) in air