重型柴油公交车实际道路颗粒物排放的理化特征

为研究重型柴油公交车实际道路颗粒物排放的理化特征,采用车载排放测试方法,选取了2辆国Ⅲ和4辆国Ⅳ柴油公交车,对气态污染物和颗粒物排放因子、粒径分布及颗粒物中的组分(包括碳组分、离子、元素和有机组分)排放特征进行了实测分析.结果表明:测试车辆的颗粒数量主要集中在100 nm以下粒径段,颗粒质量排放总体呈倒U型分布,粒径峰值位于300 nm左右.OC和EC分别占尾气颗粒物总质量的36.10%±8.94%和27.97%±10.00%,离子和元素组分分别占7.75%±1.01%和22.71%±3.09%.柴油质量对柴油车尾气颗粒物成分具有较大影响,燃用国Ⅲ柴油的车辆尾气中富含S、Ca、Mg、Na等元素组分,其主要来自燃油中的硫分和杂质.在可检出的弱极性可溶有机物中,正构烷烃和脂肪酸的含量较为丰富,分别占颗粒物总质量的1.95%和5.13%,此外还有一定量的藿烷和PAHs(多环芳烃).其中,正构烷烃组分主要分布于C19～C29,正构烷酸主要集中在C12、C14、C16和C18等偶数碳组分.国Ⅲ和国Ⅳ柴油公交车的PAHs排放因子分别为198.2、62.5 μg/km,以3环和4环PAHs为主,菲、荧蒽、芘、惹烯、苯并荧蒽、、苯并123-cd]芘和苯并苝是较为主要的PAHs组分.需要指出的是,由于采用定比例稀释方法,颗粒物中组分的测试结果可能与其实际排放存在一定偏差. 

Physicochemical Characteristics of Real-World PM Emissions from Heavy-Duty Diesel Buses

Abstract:To study the physicochemical characteristics of real-world PM emissions from heavy-duty diesel vehicles,on-road vehicle emission measurements were conducted on two China Phase Ⅲ diesel buses and four China Phase Ⅳ diesel buses using a Portable Emissions Measurement System(PEMS).Emission factors of gaseous and particulate pollutants,particle size distributions and PM chemical compositions(i.e.,carbonaceous,ionic,elemental and organic compounds) were investigated.The results showed that the major size by particle number was less than 100 nm,and the particle mass showed a U distribution pattern with peak size around 300 nm.OC and EC took up 36.10%±8.94% and 27.97%±10.00% of total particle mass emissions,respectively.Ionic and elemental components accounted for 7.75%±1.01% and 22.71%±3.09% of the total particle mass emissions,respectively.The quality of diesel fuel greatly impacted the chemical compositions of PM emissions from diesel vehicles.PM emissions from the tested vehicles fuel by China Phase Ⅲ diesel contained rich elemental components such as S,Ca,Mg and Na,which were mainly from sulfur and impurities in the diesel fuel.Among the soluble weak-polar organic compounds,n-alkanes and alkane acids had higher proportions,occupying 1.95% and 5.13% of total PM mass emissions,respectively.Besides,hopanes and PAHs also existed in the emissions.The carbon number distribution of n-alkanes mainly ranged from C19 to C29,and alkane acids exhibited obvious even carbon number predominance on C12,C14,C16 and C18.The emission factors of PAHs from China Phase Ⅲ diesel buses and Phase Ⅳ diesel buses were 198.2 and 62.5 μg/km,respectively.The major components of PAHs were tricyclic and tetracyclic PAHs including phenanthrene,fluoranthene,pyrene,retene,benzofluoranthrene,benzopyrene and benzoperylene.The particles were sampled with a constant dilution ratio,which will induce a certain bias to the actual emissions on the results of PM components.