[qwikz28]

interesting info:

Though nitrous oxide evidently leads to global warming, there have been no laws ratified to actually lower the emission of greenhouse gases, thus nitrous oxide is not seen as a pollutant. No one is sure either of how much nitrous oxide is actually produced by a catalytic converter, however one study has calculated that “…a car with a fuel economy of about 19 miles a gallon would produce .27 grams of nitrous oxide per mile.”[3] It has also been calculated that since the extinction of older cars without catalytic converters, the production of nitrous oxide has increased by nearly 50%.

source: http://www.lcc.ukf.net/kskills/catconv.htm