Size resolved composition of diesel exhaust nanoparticles

Knowledge of physico-chemical characteristics of particle emissions from combustion engines is essential for various modelling purposes and environmental analysis. It is of particular interest to obtain emission factors of intermediate-volatility organic compounds (IVOC) and semi-volatile organic compounds (SVOC) which have not been comprehensively reported in the literature due to the limitations of characterisation methods. In the current study, a multi-stage Nano impactor and the two-dimensional gas chromatography (GC×GC) mass spectrometry (MS) technique were used to comprehensively characterise size fractionated particle phase emissions from a light-duty diesel engine based on the particle size, compound groups and carbon number. The number size distributions of particles between 1.2-1000 nm were also investigated. Exhaust gas samples were taken before a diesel oxidation catalyst (DOC), after the DOC and after the DOC combined with a catalysed diesel particulate filter (DPF). In samples taken before the DOC (engine-out), the total particulate SVOC (IVOC+SVOC) emission factor was approximately 105 mg/kgf (which was ~49% of the total particle mass) and the peak concentration of different classes of SVOC was found in the particle size bins close to 100 nm where most of the total particle mass was found. Alkanes, with maximum abundance at C24, were the most dominant class of SVOC in samples taken before and after the aftertreatment devices. Total particulate SVOC emissions were removed with ~75% efficiency using the DOC and by ~92% using the DOC+DPF. Alkanes, cycloalkanes, bicyclics and monoaromatics were all removed by >90% using the DOC+DPF; however, oxygenates were removed by only ~76% presumably due to the oxidation of different species within the aftertreatment system and reappearance as oxygenates. A high concentration of particles was measured in the sub-2.5 nm range. These particles were efficiently removed by the DOC+DPF due to both the loss of semi-volatile constituents and physical filtration.

内燃机颗粒排放物的物理化学特性认知，对于各类建模应用与环境分析均具有重要意义。其中，获取中挥发性有机化合物（IVOC）与半挥发性有机化合物（SVOC）的排放因子尤为值得关注——由于表征方法的局限性，这类物质的排放数据在已有文献中尚未被全面报道。本研究采用多级纳米撞击器与二维气相色谱（GC×GC）-质谱（MS）技术，基于粒径、化合物类别与碳数，对轻型柴油发动机的粒径分级颗粒相排放物完成全面表征；同时，本研究还对1.2~1000 nm粒径范围内的颗粒粒径数浓度分布展开了探究。本研究分别在柴油氧化催化剂（DOC）上游、DOC下游，以及DOC与催化式柴油颗粒过滤器（DPF）联用系统的下游采集排气样品。在DOC上游的发动机原始排放样品中，颗粒态总半挥发性有机化合物（IVOC+SVOC）排放因子约为105 mg/kgf，约占总颗粒质量的49%；不同类别SVOC的浓度峰值出现在接近100 nm的粒径档，该区间亦是总颗粒质量的主要分布区域。烷烃是前后处理装置上下游样品中占比最高的SVOC类别，其丰度在碳数C24处达到峰值。采用DOC可实现约75%的颗粒态总SVOC脱除效率，而DOC与DPF联用系统的脱除效率可达约92%。针对烷烃、环烷烃、双环类化合物与单环芳烃类物质，DOC+DPF系统的脱除率均超过90%；但含氧化合物的脱除率仅约76%，推测是由于后处理系统内不同物种发生氧化反应，进而以含氧化合物的形式再次生成。研究还在小于2.5 nm的粒径范围内检测到较高浓度的颗粒，这类颗粒可通过DOC+DPF系统得到高效脱除，其脱除机制同时涵盖半挥发性组分的流失与物理过滤作用。

搜集汇总

背景与挑战

背景概述

该数据集聚焦于柴油发动机排放纳米颗粒的尺寸分辨组成，通过先进技术（如多级纳米冲击器和GC×GC-MS）详细表征颗粒相中的IVOC和SVOC化合物，覆盖1.2-1000 nm尺寸范围。研究发现，发动机出口总颗粒SVOC排放因子较高（约105 mg/kgf），且后处理设备（DOC和DPF）能有效去除大部分SVOC，但氧合物的去除率较低，揭示了排放特性及控制效果的关键数据。