## 4 Discussion
### Tracing of Contamination Hotspots and Presumable Emission Sources via Mapping of _gl Values_  
Taking into account the discussion above, the following 17 analytes are presumed to have at least mixed, i.e., crustal and partially anthropogenic, origin: As, Br, Ca, Cl, Cr, Cu, Fe, K, Mg, Mn, Ni, P, Pb, S, Sr, V, and Zn. Multi-panel figures were prepared for them (Figures S1-S17). Comparison of the distributions of _Igeo'N_ and _Igeo'_ values of different analytes among different _SCC_ is given in Figure 14: the higher the value of \(n\), the better the index for revealing hotspots. It seems that from two alternative _Igeo_ indices, _Igeo'N_ was the better choice to reveal hotspots, since respective \(n\) values of As, Cl, Cr, Fe, Mg, Mn, Ni, S, Sr, and V were higher, the only exception being Pb. The wider spread (more _SCC_ intervals) of _Igeo'N_ distribution was determined by lower _Bn_ values than _Cv_ values (Table S2). For example, for Cl, its _Bn_ = 99 \(\mu\)g g\({}^{-1}\) and _Igeo'N_ was distributed among seven _SCC_ intervals, while its _Cv_ = 370 \(\mu\)g g\({}^{-1}\) was higher; therefore, _Igeo'_C values were found only in five _SCC_ intervals. The _aE'N_ values found in the interval 1-1.5 enabled us to draw attention to K as possible pollutant. Meanwhile, according to _Igeo'N_ it could remain unnoticed (Figure S8). The judgement about prevailing natural, mixed or anthropogenic origin of elements according to _nEF_ indices also depended on _THR_ values. If evaluation was according to _nEF_'_C_ and the lower _TRH_ was 1, while the upper one was 10, five dust sampling sites according to Mg and one according to Cr would be assigned to those having prevailing natural origin (Figure 15). Meanwhile 14 analytes which can be suspected for significant anthropogenic sources can be arranged in the following sequence according to the number of sites where the index exceeds 10: Br, Cu, S, Zn (20 sites for each) > Ca, P (19) > Cl, Pb (18) > Fe (12) > Cr (11) > As (5) > Ni (4) > Sr, K (1). But if we selected the lower _THR_ equal to 10 which was proposed in [40] for attribution to prevailing crustal origin, the number of analytes with such possible origin would increase from aforementioned two to 13. The analytes can be arranged according to decreasing number of such sites as follows: V, Mn, Mg (20 sites for each) > Sr, K (19) > Ni (16) > As (15) > Cr (9) > Fe (8) > Pb, Cl (2) > Ca, P (1). However, if we take into account the upper _THR_ equal to 20 proposed in [40] for judgement about anthropogenic origin, K will be lost from aforementioned list of 14 elements, while another 13 analytes will be arranged according to decreasing number of such sites as follows: Zn (20) > Br (19) > Cu, S (>18) > P (15) > Cl (14) > Fe (11) > Cr (10) > Pb (8) > Ca, As (3) > Sr, Ni (1). Figure 14: The frequency distribution of elemental _Igeo’N_ and _Igeo’_C values of twenty TSP sampling sites in seven so-called contamination classes SCC. Explanation: log2(x) column indicates the threshold values of _SCC_ intervals for logarithmic data, while x column shows respective values for non-logarithmic data. \(n\) is the total number of _SCC_, in which the scatter of occurrences was found. If evaluation of the analyte origin is done according to \(nEF\)'\(Al\)'\(N\) and the lower \(THR\) is 1, while the upper \(THR\) is 10 (it is the same according to common publications [45; 46; 47] and publication of [PERSON] et al. [40]) Mg in four sites and Cr in one site would be attributed to prevailing natural origin. Meanwhile, the analytes suspected for mainly anthropogenic origin would be arranged in the following sequence: Ca, Cu, Zn (20) \(>\) Cl, P (19) \(>\) S (18) \(>\) Fe, Cr (12) \(>\) Ni (11) \(>\) Br (8) \(>\) As (3) \(>\) Pb, Sr (2) \(>\) V (1). However, if the lower \(THR\) equal to 5 proposed in [40] was selected, the number of analytes with prevailing natural origin would be higher and they would be arranged in the following sequence: K (19) \(>\) Mg (16) \(>\) Mn (13) \(>\) Pb (11) \(>\) V (8) \(>\) Sr (7) \(>\) Cr, Fe (5) \(>\) Ni, Br (3).