## 4 Discussion
### Differences in Geochemical Pattern of the City Areas  
To identify the hotspots and emission sources of contaminants, the indices _Igeo'C_, _Igeo'N_, _aE'N_, _nEF'AI'C_, and _nEF'AI'N_ were used for comparison of geochemical pattern of two areas: the \(<\)1 km area which includes sampling sites located near iron ore stevedoring, i.e., at closer than 1 km distance, and the \(>\)1 km area which includes sites from the rest of city, i.e., located further than 1 km from iron ore stevedoring. When searching by the U-test for the differences in geochemical pattern of \(<\)1 km (twelve sampling sites: 3, 4, 11-20, Figure 1) and \(>\)1 km (six sampling sites: 1 and 2, 5, 6, 7, 8 and 9, 10, in paired sites 1 and 2 and 8 and 9, the data were averaged), the findings of Section 4.2 were taken into account: for Cl, S, Sr, Ni, Br, V, and Zn, only data of period P3 were used, since an additional 10 samples (sites 11-20) at \(<\)1 km distance from iron ore stevedoring were taken namely during this period. Comparison of separate objects of investigation, e.g., cities, enterprises, sites from different functional or landscape zones, is common in dust research [8,34,80,82]. Different formulas of _Igeo'N_ and _aE'N_ inevitably lead to different median values in two city areas. Despite this, \(p\)-values indicating the significance of the differences between the \(<\)1 km and \(>\)1 km areas in the values of each of two indices are absolutely the same for 14 analytes (As, Cr, Cu, V, Zn, S, Ca, Fe, K, Mg, Mn, Sr, Zr, and Br) and only slightly differ for the remaining eight analytes (Table S7). Therefore, for each analyte both indices lead to identical conclusions about significant or insignificant differences between the areas: \(p\)-values of both _Igeo'N_ and _aE'N_ indicate that dust in the \(<\)1 km area is significantly (\(p<0.05\)) enriched in Fe and Cr, while the values of Mg, Ca, Zr, Si, Al, Cu, Rb, Sr, Ti, and K indices are lower in comparison with dust in the rest of the city (\(>\)1 km). We shall use only _aE'N_ for comparison of median values of analytes in two areas (\(<\)1 km and \(>\)1 km) with the help of their ratio, since the analogous comparison of _Igeo'N_ needs additional more complicated mathematical transformation of log data. We found that the median _aE'N_ values of Fe and Cr in dust from the \(<\)1 km area more than 3.5 times exceed respective values from the rest city (\(>\)1 km) (Figure 12). On the contrary, the median values of _aE'N_ in dust from the \(>\)1 km area which is more distant from Fe ore stevedoring are from 2.0 to 6.2 times higher for K, Sr, Ti, Rb, Cu, Al, Si, Zr, Ca, and Mg. The indices \(nEF^{\prime}Al^{\prime}C\) and \(nEF^{\prime}Al^{\prime}N\) based on normalization by Al (the main indicator of claycy component of soil-forming rocks in the study area), allow to highlight the anthropogenic part of the analyzed analytes by reducing their pedogenic constituent (Table S8). Despite different formulas and different median values for each analyte, both alternative \(nEF^{\prime}Al\) indices have much in common: (a) identical \(p\)-values obtained comparing the differences between two areas according to each index, (b) identical ratios of the median values of selected index in the \(<\)1 km to the \(>\)1 km areas. This is not surprising because in each analysis site, the same unique \(Cv\) or \(Bn\) value is used in the denominator. Whichever of these two indices is used to reveal the differences between two areas by the U-test, the results are identical: the \(<\)1 km area was significantly enriched not only in Fe and Cr, but also in As, Pb, S, Mn, Br, and Cl. Therefore, additional contamination by these elements from the source in this area can be hypothesized (Figure 13). Figure 12: Ratios of median elemental \(aEN\) values in two areas. Legend: \(<\)1 km/\(>\)1 km (in brown) indicates accumulation of analytes in iron ore stevedoring dust in the \(<\)1 km area, while \(>\)1 km/\(<\)1 km (in green) their accumulation in the rest part of the city.