A substance whose presence changes the rate of chemical reaction without itself undergoing permanent change in its composition. Catalysts may be accelerators or retarders. Most inorganic catalysts are powdered metals and metal oxides, chiefly used in the petroleum, vehicle, and heavy chemical industries.

A colorless, odorless gas produced by the incomplete combustion of fuels with a limited oxygen supply, as in automobile engines. According to the U.S. Environmental Protection Agency, CO contributes to the formation of smog ground-level ozone, which can trigger serious respiratory problems.

A product of combustion that has become an environmental concern in recent years. CO2 does not directly impair human health, but is a greenhouse gas that traps the Earth's heat and contributes to the potential for global warming.



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