Small Opel, Honda, Nissan and Volkswagen cars emit the least polluting exhaust fumes of the 76 models sold in Sweden, an authoritative Swedish motor magazinesaid this week. Big BMWs, Porsche sports cars and a brand new Saab model were the worst polluters in a test, which measures emissions of carbon monoxide, carbon dioxide and nitrogen dioxide as well as hydrocarbons, sulphur dioxide and other polluting particles, the Teknikens Varld magazine said.