Nonvolatile ultrafine particles observed to form trimodal size distributions in non-road diesel engine exhaust

Abstract

Some recent findings regarding the negative health effects of particulate matter increase the relevance of the detailed characteristics of particulate emissions from different sources and especially the nonvolatile fraction of particles. In this study, the nonvolatile fraction of ultrafine particulate emissions from a non-road diesel engine was studied. The measurements were carried out in an engine laboratory and the exhaust sample was taken from the engine-out location with various steady state driving modes. Four different fuels, including fossil fuel, soybean methyl ester (SME), rapeseed methyl ester (RME), and renewable paraffinic diesel (RPD), were used. In the sampling system, the sample was diluted and led through a thermodenuder removing the volatile fraction of particles. The measured particle size distributions of nonvolatile particles were found to be trimodal. Based on the size distribution data as well as the morphology and elemental composition of particles in transmission electron microscopy (TEM) samples, we were able to draw conclusions from the most probable origin of the different particle modes, and the modes were named accordingly. From larger to smaller in particle size, the modes were a soot mode, lubricating oil originated core (LC) mode, and a fuel originated core (FC) mode. All of these three modes were detected with every driving mode, but differences were seen, for example, between different fuels. In addition, a trade-off was observed in the concentrations of the LC mode and the soot mode as a function of the engine torque.

Contribution of traffic-originated nanoparticle emissions to regional and local aerosol levels

“…The parameters of the fit are presented in Table 1. It is interesting that trimodal size distributions of non-volatile particles-with quite similar particle sizes to the ones found in this study-were also detected in diesel exhaust by Kuuluvainen et al (2020), who conclude that the mode in the middle is originated from lubricating oil, whereas it is here associated with nucleation-originated particles. The contribution of the road transport-related particle number emissions (from the PMF factor 6) to the total emissions from the all emission sources was averagely 8 % in the original inventory.…”

“…Therefore, a trimodal fit suits well in separating particle composition between the three sources. However, it should be noted that the vehicle exhaust particle formation is a complex process and this approach is only an approximate; e.g., Kuuluvainen et al (2020) and Alanen et al (2020) (Lintusaari et al)) and, secondly, assuming the nucleation mode composition for the remaining volatile part. The non-volatile part is assumed to be BC due to the lack of more specific information.…”

Particle Number Emissions of Gasoline, Compressed Natural Gas (CNG) and Liquefied Petroleum Gas (LPG) Fueled Vehicles at Different Ambient Temperatures

“…In addition, for a gasoline and diesel vehicles, detected~10 nm particle population is connected to lubricant additives and a slightly smaller, coexisting particle mode to fuel characteristics [26][27][28]. The <23 nm particle composition in vehicle exhaust is, in general, proposed to include aliphatic or polycyclic aromatic hydrocarbons, metals originating from lubricant oil additives or in-cylinder wear or fragmented soot particles [23,[26][27][28][29][30][31][32][33]. The small particle size and the composition of the vehicle exhaust particles are often connected to potential adverse health effects in inhalation exposure [34][35][36][37][38][39][40][41].…”

“…CNG fueled ship engine exhaust particle population is suggested to include three different solid particle modes: soot mode at 30 nm to 70 nm size range, lubricant originating particle mode at size range from 10 nm to 30 nm and fuel originating particle mode in <10 nm size range [23]. In addition, for a gasoline and diesel vehicles, detected~10 nm particle population is connected to lubricant additives and a slightly smaller, coexisting particle mode to fuel characteristics [26][27][28]. The <23 nm particle composition in vehicle exhaust is, in general, proposed to include aliphatic or polycyclic aromatic hydrocarbons, metals originating from lubricant oil additives or in-cylinder wear or fragmented soot particles [23,[26][27][28][29][30][31][32][33].…”

Contribution of traffic-originated nanoparticle emissions to regional and local aerosol levels

“…Anthropogenic emissions overall can also greatly affect the frequency and intensity of NPF events in urban air (Saha et al, 2018). Additionally, emissions of diesel vehicles can include metal-containing particles, which can be found in a separate size mode from non-volatile particles near 10 nm (Kuuluvainen et al, 2020). Metallic combustion-originated nanoparticles have also been found to exist in the brains (Maher et al, 2016).…”