## 4 Conclusions  
* This study assessed whether it is possible to quantitatively evaluate the accumulation status of soot and ash utilizing the CR X-ray imaging technique and ImageJ J. Respective X-ray images were taken after cumulating carbon powder, similar to soot, on the DPF substrate, in quantities of 12.5 g, 25 g, 62.5 g, 100 g and 125 g. Later, X-ray images were filmed after placing 12.5 g, 25 g, 100 g, and 125 g of ash powder in a new substrate to conduct a comparative analysis of the produced images. * As the accumulated carbon powder and ash powder increased in quantity, the images of carbon powder accumulation showed the upper part of the plug of the substrate  
Figure 10: Pixel values comparison of carbon powder and ash powder. being colored paler white, whereas those of ash powder displayed deeper white color. An analysis of the pixel values using the histogram and ROI features of Image J confirmed that ash powder had a higher pixel value than carbon powder did. As ash demonstrates a higher density than that of carbon powder due to their composition of components deriving mainly from engine oil, it leads to a lower X-ray transmittance, which is presumed to make the images appear whiter. * This study confirms that it is possible to identify the accumulation status of soot and ash on the DPF substrate. However, although the qualitative evaluation was verified, additional uncertainty studies are needed to verify the quantitative evaluation. In addition, further research is required on the accumulation analysis of soot and ash on the DPF of an in-use vehicle with canister and verification activities on the economic aspects and safety. Conceptualization, S.L. ; Methodology, G.P. and M.K. ; investigation, M.K. and H.R. ; Supervision, S.L. ; Writing--original draft, G.P. and H.R. ; Writing--review and editing, G.P., H.R. and S.L. All authors have read and agreed to the published version of the manuscript. This research was supported partly by the Korea Environment Industry & Technology Institute (KEITI), through the Reduction Management Program of Fine Dust Blind-Spots grant funded by the Korea government (MOE; Ministry of Environment) (No. 2020003070001) and partly by the National Research Foundation (NRF), Korea, through BK21 Program grant funded by the Korea government (MOE; Ministry of Education) (No. 5199990814084). Not applicable. All necessary data have been reported in this article and there are no other data to share. The authors thank the research scientists at the Korea University Department of Health Safety Convergence Science for their assistance in this study. The authors declare no conflict of interest. The following abbreviations are used in this manuscript:  
DFP & & & & & & & & & & & & & & & & &  
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