But the new cleaner fuel has come on stream just as regulators are clamping down on emissions of smog-causing nitrous oxides and soot-like particulates, which have been linked to lung cancer.

• 不过这种更干净的燃料一直没能投入生产，直到决策者们决定限制一氧化碳和灰尘微粒的排放量（它们是有害烟雾的主要来源，煤尘微粒则与肺癌有联系）。