## 3 Results and Discussion
### Analysis of Elemental Compositions in Urban PMs and Incineration Asl
#### 3.3.2 Analysis of Elements of Incineration Ash and Urban PMs by the WD-XRF Method
For example, in the case of Pb and Zn, both come from the metal processing industry, but they are also related to automobile emissions [54]. As the source of Cu is vehicle (brake wear) [3; 54] and industrial (combustion in smelting furnaces) emissions [53], its exact contributions cannot be easily determined. Among the various elements present in dust, Al, As, Fe, Ti, Mn, etc. originate from not only natural sources (crust, desert, air mass transport, volcanic emission) but also anthropogenic origins [23; 60]. A recent source apportionment study revealed that the main anthropogenic sources contributing to the concentrations of toxic metallic elements are vehicle and industrial emissions [3]. Based on these results, this work carefully concluded that relative to that in NIST SRM 1648a (St. Louis is an industrial township in Missouri, USA [51], and NIST SRM 1648a dust was collected in 1976-1977 [35]), the effect of vehicular emission in the KRISS urban dust CRM candidate (collected in 2019) is greater than the effect of industrial activity. In addition, the concentrations of toxic metallic elements seem to decrease in the KRISS urban dust as the use of toxic elements drops due to environmental regulations. The mass fractions of REEs, U, and Th in the KRISS urban dust CRM candidate obtained through the \(k_{0}\)-INAA method were compared with those in NIST SRM 1648a (Figure 5). The REEs, U, and Th are soil/crustal-originated metals, such as Al, Ba, Ca, Mg, and Sr [4]. The presence of REEs is attributed to local crustal contributions when the relative levels are Ce > La > Sm [23; 60]. The same trend was observed for NIST SRM 1648a and KRISS urban dust. This result indicated that lanthanide elements originated from natural sources [60]. The mass fractions of REEs in the KRISS urban dust CRM candidate tend to be slightly high relative to those in NIST SRM 1648a, except for the Eu element. In the case of U and Th, the opposite tendency is shown in Figure 5, that is, Th is high in KRISS urban dust, and U is slightly high in NIST SRM 1648a. It would be interesting to know the concentrations of U, Th, and REEs for observation of natural radioactivity [65] and abundance patterns in the environment [66]; however, their analysis is also important in terms of improving the accuracy of the overall analysis. In SC-INAA, only the elements of interest are analyzed (interference elements are excluded). Thus, correcting the nuclear product or nuclear interference experimentally is not possible. For example, the \({}^{235}\)U(n\(\
eq\)) fission products, which contribute to \({}^{95}\)Zr, \({}^{95}\)Nb, \({}^{97}\)Nb, \({}^{99}\)Mo, \({}^{99m}\)Tc, \({}^{139}\)Ba, \({}^{140}\)La, \({}^{141}\)Ce, and \({}^{147}\)Nd isotopes, must be corrected [24; 30], but their nuclear interference could not be corrected if the U concentration were unknown. In another example, the \({}^{26}\)Mg(n,\(\gamma\))\({}^{27}\)Mg reaction competes with the \({}^{27}\)Al(n,p)\({}^{27}\)Mg via nuclear isotope interference reaction (threshold reaction with fast neutrons); hence, the amount of Al must be determined to establish the accurate concentration of Mg [19; 27; 31]. The \(k_{0}\)-INAA method is a multi-elemental analysis approach that analyzes interference elements, such as U and Al, together without the need to prepare standards. Hence, the primary nuclear interference can be corrected accurately with this method.