Please answer the following question: Background: Gasoline-powered vehicles emit a lot of harmful materials. Nitrogen oxides are formed when atmospheric nitrogen reacts with oxygen at the high temperatures found in a car engine. Carbon monoxide is a by-product of incomplete combustion of hydrocarbons. Evaporated and unused fuel releases volatile hydrocarbons into the atmosphere to help form smog. The presence of a catalytic converter in the exhaust system of the car causes these materials to react and be changed into less harmful products. Paragraph: Blue island and Red island were two big sister islands situated 100 miles from each other. People on Blue island used gas powered vehicles, while people on Red island used electrical vehicles. The people on Blue island presented more respiratory problems. Given the paragraph above, please answer correctly the following question: Which island emitted more harmful materials?
A:
Blue