The technology of biomass pyrolysis can convert low-quality biomass into bio-oil that has the character of high-quality, high energy density, cleanness and zero carbon dioxide emission.

大力开发生物质的热裂解制油技术，可将低品位的生物质能转化成高品质的、高能量密度，清洁、无污染而且二氧化碳排放为零的生物油液体燃料。

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So although the cars are technically zero emission, the process of making the hydrogen produces carbon dioxide.

BBC: Apollo's fuel-cell power legacy