*3.6. Scanning Electron Microscope with Energy Dispersive Spectroscopy (SEM-EDS)*

More in-depth information was obtained using SEM-EDS that makes it possible to study the elementary analysis of the PM. Figure 11 shows morphology of the PM for diesel end petrol engines. It can be seen that particles deposited on the Diesel engine fibers are smaller, and their amount is lower (Figure 11a,b) than in case of petrol engine (Figure 11c,d). PM from the petrol engine showed more agglomerations. SEM observations in AsB mode

showed different weight of the collected contaminations (heavier particles shines). EDS analysis described below reveals that shining objects are iron particles.

**Figure 9.** EGA results for petrol engine, where (**a**) presents DSC-TG signals, and (**b**) shows QMS registered signals.

**Figure 10.** EGA results for Diesel engine, where (**a**) presents DSC-TG signals, and (**b**) shows QMS registered signals.

**Figure 11.** SEM images for Diesel engine in SE2 mode (**a**), and AsB mode (**b**); petrol engine (scooter) in SE2 mode (**c**), and AsB mode (**d**); pure filter in SE2 mode (**e**) and AsB mode (**f**).

The example of EDS area chosen from SEM micrographs for the Diesel and petrol (scooter) engine is shown in Figure 12.

**Figure 12.** SEM micrographs for (**a**) Diesel engine and (**b**) petrol engine (scooter), showing area of EDS analysis. Elemental analysis for (**c**) Diesel and (**d**) scooter.

SEM-EDS analysis enabled to quantitatively assess the elemental analysis of PMs from the Diesel and petrol engine (Table 3). EDS analysis indicates that the main component of PMs from both engines is carbon (most probably from organic compounds originated from combustion process). The small amount on the pure filter is the effect of covering the filter by very thin layer of carbon (6 nm) before SEM-EDS imaging. The amount of oxygen is similar to the pure filter in the case of the Diesel engine, and it is significantly smaller for the petrol engine: this phenomenon can be the effect of covering filter fibers by carbon agglomerates in the case of the petrol engine and more distracted particles in the case of Diesel engine that do not stick the filter fibers. This phenomenon is also present in the case of Na, Ca, Si, Al, and Mg. Surprisingly, sulfur is present in the case of PMs from both engines, on a similar level that can come from some engine parts/oils. Only for PMs for Diesel engine was Fe noticed.


**Table 3.** Elemental Analysis of filters from Diesel and petrol engines.

To compare these results with other available studies, it can be seen that, in research of Güney and Aladag [39], where gasoline-fueled vehicles were tested in terms of chemical analysis of particulate matter; in particular, SEM analyses show that PM is formed by solidification and agglomeration [39]. In this publication, the SEM analysis also showed that PM from gasoline engines shows more agglomerations, which was mentioned in point 3.6. In research of Güney and Aladag, the EDS analysis allowed for indicating 20 elements of PM: C, F, N, Na, O, Mg, Br, Si, Hg, S, P, Pb, Ca, Cr, Mn, Fe, Ni, Co, Cu, and Zn [39]. Some of the elements were also detected in SEM-EDS analysis in this paper, which is shown in Figure 12 and Table 3. Yang et al. [40] investigated the chemical composition of fine particulate matter emitted by gasoline and diesel vehicles, and this research showed that the most dominant components of PM2,5 for the Diesel and gasoline vehicle were carbonaceous species [40]. Research of Yang et al. also investigated that the top five metal elements in PM2,5 were Na, Ca, Fe, Zn, and Al, which also can be confirmed by studies of Cheung et al. [41] and Hao et al. [42].
