## 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  
Some of the chemical fingerprint elements (P, Si, Ni, and Pb) for source identification that are difficult to analyze with the \(k_{0}\)-INAA method were analyzed with WD-XRF. The detailed results are shown in Table 3 and were compared to NIST SRM certified values or ID-ICP/MS results. The expanded uncertainties (\(k=2\)) in Table 3 and Table S2 were calculated from combined uncertainty at \(1\sigma\) included the contribution factors of statistical error (0.5\(-10\%\)), instrument error (1%), calibration curve error (1%), and fusion bead preparation (2%) [49]. The source apportionment study of metallic elements demonstrated that the generation of Pb was related to a combination of two anthropogenic causes, namely, steel/smelting activity and vehicle emissions [3]. As lead was banned as a fuel additive in the USA in 1996, the Pb concentration in dust seems to have decreased significantly with Br (lead scavenger) concentration [19; 50; 51]. NIST SRM 1648a urban dust contains 6550 mg/kg of Pb, whereas KRISS urban dust contains only less than 150 mg/kg. Ni and Pb elements are related mainly to the combustion of fossil fuels, and even after the ban on the use of additives, these elements are still present in airborne PM [3; 8; 19; 52; 53]. Si is a typical soil component (Earth's crust) similar to Al, Ca, Fe, and Mg, and its contribution comes from soil-derived particles [1; 54]. Therefore, Si has a high mass fraction of over 12% in dust and ash, as shown in Table 3. The main origin of atmospheric P is windblown soils, biogenic emissions, and ash from biomass combustion. It is also known to originate from industrial and mining emissions [55; 56]. In KRISS urban dust, the concentration of P is higher than that in NIST SRM 1648a (8410 mg/kg vs. 1100 mg/kg). The P level in KRISS ash is significantly high (70,907 mg/kg) due to the contribution of the incineration process. The atmospheric transport of P is an important mechanism for delivering nutrients to lake ecosystems [55], but it can also cause eutrophication problems when present in excess [57]. The mass fractions of other elements analyzed by WD-XRF are shown in the Supplementary Materials (Table S2) and compared with \(k_{0}\)-INAA results. The percentage deviations between two methods are within 10% except few elements (i.e., trace or minor level). Comparison of NIST SRM 1648a Urban PM and KRISS Urban Dust CRM Candidate: Element Composition and Source Contribution  
In the KRISS urban dust CRM candidate, 46 elements were analyzed using \(k_{0}\)-INAA method, and the concentration levels for all elements were compared with those of NIST SRM 1648a (Table 2). NIST SRM 1648a is an urban PM that was collected from St. Louis, USA in 1976-1977 [35]; St. Louis is an industrial area in the state of Missouri [51]. The KRISS urban dust CRM candidate is the dust collected from air-ventilation filters installed on top of the buildings in metropolitan areas (Seoul/Gyeonggi-do City) in South Korea in 2019. The KRISS urban dust sample is a time-integrated sample (no seasonal or temporal variation information) similar to NIST SRM 1648a. The sample does not represent specific areas or sources from which it was collected; rather, it reflects the atmospheric dust of urban areas in South Korea. The sample collection locations are mixed residential, commercial, and industrial areas. Figure 4 shows the gamma-ray spectra of short-lived nuclides irradiated for 2 min after cooling times of ~11 and ~34 m and those of the long-lived nuclides irradiated for 12 h after cooling times of ~3, ~9, and ~29 days. In the comparison of the mass fractions of the two types of airborne PM, the elements in the KRISS urban dust CRM candidate that showed a high concentration as compared to NIST SRM 1648a are Au (+904%), Cl (+167%), Na (+233%), W (+412%), and Zn (+357%).