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
21st-century fossil fuel regulations in the United States are subject to New Source Review (NSR) and Prevention of Significant Deterioration (PSD). Emissions from these plants have the largest contributions of sulfur dioxide (SO2) and nitrogen oxides (NOx) into the atmosphere. Facilities in the electric sector are restricted to emission standards defined by the Clean Air Act (United States). While monitoring and controlling environmental releases of plants has been difficult, the EPA has been enforcing their policies regarding air quality over the last decade under President Barack Obama. While the Clean Air Act postulates regulations and rules limiting the emissions of greenhouse gases, other laws are concerned with standards