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NOx is a generic term for the various oxides of nitrogen produced during combustion. They are believed to aggravate asthmatic conditions, react with the oxygen in the air to produce ozone, which is also an irritant and eventually form nitric acid when dissolved in water, a form of acid rain.

Three primary sources of NOx formation in combustion processes are documented: prompt NO, fuel NO and thermal NO. Thermal NOx formation, which is highly temperature dependent, is recognized as the most relevant source when combusting natural gas.

Technologies such as flameless oxidation (FLOX) and staged combustion significantly reduce thermal NOx in industrial processes.

The Environmental Protection Agency (EPA) regulates and enforces NOx emission limits in the U.S. in accordance to legislation passed by Congress.

The Kyoto Treaty, ratified by 54 nations in 1997, calls for a substantial world wide reduction of green house gas including NOx.\n