Fuel cells offer several advantages: they do not have moving parts and there is no burning involved, so there are negligible emissions of environmentally harmful gases like nitrogen, sulfur oxide and carbon monoxide.

FORBES: Magazine Article

For important pollutants monitored by the EPA, natural gas power cuts carbon monoxide emissions by 81%, nitrogen oxide emissions by 80%, sulfur dioxide emissions by 99%, mercury emissions by 100%, and particulates by 99%.

FORBES: The Sierra Club Fails An Environmental Consistency Test