Vehicle exhaust is one of the major organic sources in urban areas. Old taxis equipped with failed three-way catalysts (TWCs) have been regarded as “super emitters”. Compressed natural gas (CNG) is a regular substitution fuel for gasoline in taxis. The relative effect of fuel substitution and TWC failure has not been thoroughly investigated. In this work, vehicle exhausts from gasoline and CNG taxis with optimally functioning and malfunctioning TWCs are sampled by Tenax TA tubes and then analyzed by a comprehensive two-dimensional gas chromatography-mass spectrometer (GC×GC–MS). A total of 216 organics are quantified, including 80 volatile organic compounds (VOCs) and 132 intermediate volatility organic compounds (IVOCs). Failure of TWC introduces super emitters with 30 – 70 times emission factors (EFs), 60 – 112 times ozone formation potentials (OFPs), and 34 – 92 times secondary organic aerosols (SOAs) more than normal vehicles. Specifically, for the taxi with failed TWC, the total organic EF of CNG is 16 times that of gasoline, indicating that the failure of TWC exceeds the emission reduction achieved by CNG-gasoline substitution. A significant but unbalanced reduction of ozone and SOA is observed after TWC, whereas a notable “enrichment” in IVOCs was observed. Naphthalene is a typical IVOC component strongly associated with CNG-gasoline substitution and TWC failure, which is lacking in current VOC measurement. We especially emphasize that there is an urgent need to scrap vehicles with failed TWCs in order to significantly reduce air pollution.

中文翻译：

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三效催化剂（TWC）失效会产生“超级排放物”


汽车尾气是城市地区主要的有机污染源之一。配备失效三效催化剂（TWC）的旧出租车被视为“超级排放者”。压缩天然气 (CNG) 是出租车中汽油的常规替代燃料。燃料替代和 TWC 故障的相对影响尚未得到彻底研究。在这项工作中，通过 Tenax TA 管对具有最佳功能和故障 TWC 的汽油和 CNG 出租车的车辆尾气进行采样，然后通过综合二维气相色谱-质谱仪 (GC×GC-MS) 进行分析。总共对 216 种有机物进行了定量，其中包括 80 种挥发性有机化合物 (VOC) 和 132 种中挥发性有机化合物 (IVOC)。 TWC 失效后，超级排放物的排放因子 (EF) 是普通车辆的 30 – 70 倍，臭氧形成潜势 (OFP) 是普通车辆的 60 – 112 倍，二次有机气溶胶 (SOA) 是普通车辆的 34 – 92 倍。具体来说，对于TWC失效的出租车，CNG的总有机EF是汽油的16倍，表明TWC失效超过了CNG汽油替代所实现的减排量。 TWC 后观察到臭氧和 SOA 显着但不平衡的减少，而 IVOC 显着“富集”。萘是一种典型的 IVOC 成分，与 CNG 汽油替代和 TWC 失效密切相关，而目前 VOC 测量中缺乏这一点。我们特别强调，迫切需要报废 TWC 不合格的车辆，以大幅减少空气污染。