State Environmental Protection Key Laboratory of Vehicle Emission Control and Simulation, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; Vehicle Emission Control Center, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
State Environmental Protection Key Laboratory of Vehicle Emission Control and Simulation, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; Vehicle Emission Control Center, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
Environ Int. 2024 Aug;190:108945. doi: 10.1016/j.envint.2024.108945. Epub 2024 Aug 10.
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.
车辆尾气是城市地区主要的有机污染源之一。装有失效三效催化剂（TWC）的老旧出租车被认为是“超级排放源”。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 失效的相对影响尚未得到彻底研究。在这项工作中，通过 Tenax TA 管采集了汽油和 CNG 出租车的尾气，这些出租车的 TWC 功能正常和失效，并通过综合二维气相色谱-质谱联用仪（GC×GC-MS）进行了分析。共定量了 216 种有机物，包括 80 种挥发性有机化合物（VOCs）和 132 种中等挥发性有机化合物（IVOCs）。TWC 失效会引入超级排放源，其排放因子（EF）是正常车辆的 30-70 倍，臭氧形成潜能（OFP）是正常车辆的 60-112 倍，二次有机气溶胶（SOA）是正常车辆的 34-92 倍。具体来说，对于装有失效 TWC 的出租车，CNG 的总有机 EF 是汽油的 16 倍，这表明 TWC 失效超过了 CNG-汽油替代带来的减排效果。TWC 后臭氧和 SOA 的显著但不平衡的减少，而 IVOCs 则明显“富集”。萘是一种与 CNG-汽油替代和 TWC 失效密切相关的典型 IVOC 成分，目前的 VOC 测量中缺少这一成分。我们特别强调，迫切需要淘汰装有失效 TWC 的车辆，以显著减少空气污染。
