## 3 Results
### Principal Component Analysis (PCA)  
The relations among elements in collected moss, sampling season, modelled PM and site orientation were further investigated using PCA. According to the results, the first two dimensions express 63.07% of the total inertia, which is a significantly greater amount of inertia than the reference value of 32.89% obtained by the 0.95-quantile of inertia percentages distribution (simulation of 940 normal-distribution data tables of similar size). Thus, the description is focused on the first two dimensions. Individual sampling sites orientation in the first factor plane is presented in Figure 7 together with the supplementary qualitative variables and distance from the predominant source. The correlation circle of the active quantitative variables is presented in Figure 8.  
Figure 7: PCA results, first factor plane. Season, prevailing wind relative to the factory and distance from the factory are plotted as supplementary variables. The first dimension is positively correlated with the clr-transformed concentrations of C (r = 0.91), H (r = 0.91), N (r = 0.86), Zn (r = 0.86), Cd (r = 0.76) and one quantitative supplementary variable--distance from the factory (r = 0.74). It is negatively correlated with clr-transformed concentrations of V (r = -0.86), As (r = \(-\)0.82), Cr (r = \(-\)0.81), Al (r = \(-\)0.78), Fe (r = \(-\)0.68) and two quantitative supplementary variables--modelled concentrations of PM\({}_{10}\) in winter (r = \(-\)0.58) and modelled concentrations of PM\({}_{10}\) in summer (R = \(-\)0.55). Wilks test also indicates association of the axis with wind direction (\(p\) = 0.018), with the sites downwind tending to have negative scores on this axis while those not downwind tending to have positive scores. This suggests that the first dimension grouped elements exhibiting a spatial gradient with decreasing PM concentration and increasing distance from the factory (V, As, Cr, Al, Fe)--negative correlation, and those with opposite spatial distribution (Zn, Cd, N) with positive correlation. Pollutants in the respective groups also most likely originate in a different type of source. While the negatively correlated group of elements suggests metallurgical processes, the opposing group seems to be associated with coal combustion [99; 100; 101; 102]. A positive correlation of C and H in this group can indicate the change of the environment with increasing distance from the source toward a more natural landscape and thus more favourable conditions for growing. The second dimension is positively correlated with the clr-transformed concentrations of Pb (r = 0.93), and, to a lesser extent, Fe (r = 0.51) and Hg (r = 0.48) while negatively correlated with clr-transformed concentrations of Ni (r = \(-\)0.68) and Sb (r = \(-\)0.56). [PERSON] test result indicates a strong association of the axis with the season (\(p\) = 0.001), with the October samplings having positive scores on the axis and those sampled in June having negative scores. The second dimension grouped elements with a strong association to the season--Pb and Ni--suggesting, once again, a different origin of pollution; probably sintering for the positively correlated elements and steelmaking for negatively correlated ones [99; 100; 101]. Original, untransformed, concentration data of selected elements were plotted over the PCA results to illustrate their relationship to the two first dimensions and, thus, to wind and distance from the factory--associated with the first axis--and season--associated with the second axis (Figure 9). The only elements correlated with the first axis alongside the gradient of distance (positive correlation) were C (r = 0.75) and H (r = 0.73), which tended to have higher concentrations in samples the furthest from the predominant source. Negatively correlated were concentrations of V (r = \(-\)0.85), Al (r = \(-\)0.72), Cr (r = \(-\)0.69),  
Figure 8: PCA results, first factor plane. Correlation circle of the (clr-transformed) concentrations of elements (in black) and untransformed data (in blue).