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
Mixed oxides of nitrogen Mixed oxides of nitrogen Mixed oxides of nitrogen (MON) are solutions of nitric oxide (NO) in dinitrogen tetroxide/nitrogen dioxide (NO and NO). It may be used as an oxidizing agent in rocket propulsion systems. A broad range of compositions is available, and can be denoted as MON"i", where "i" represents the percentage of nitric oxide in the mixture (e.g. MON3 contains 3% nitric oxide, MON25 25% nitric oxide). An upper limit is MON40 (40% by weight). In Europe MON 1.3 is mostly used for rocket propulsion systems, while the NASA seems to prefer MON 3. A higher percentage of NO