## 3 Results and Discussion  
### Contents of Pollutants in Roof Runoff  
The contents of 10 of 31 examined parameters (i.e., As, B, Co, Cr, Fe, Hg, Li, Mn, Ni and Se) were below the limit of quantification (LOQ) in the majority of the roof runoff samples (Table S5), and thus, they are not considered in further data analysis and discussion in this section. The contents of the remaining 21 investigated elements, measured in the Krakow roof runoff samples, during the sampling campaign from May 2019 to February 2020, are presented in Table 1.  
\begin{table} \begin{tabular}{l l c c c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multirow{2}{*}{**Unit**} & \multirow{2}{*}{**Min**} & \multirow{2}{*}{**Max**} & \multirow{2}{*}{**Mean** \({}^{*}\)} & \multicolumn{2}{c}{**Dinking Water**} & \multicolumn{2}{c}{**Drinking Water**} & \multicolumn{2}{c}{**Drinking Water**} & \multicolumn{2}{c}{**Surface Water**} & \multicolumn{2}{c}{**Harmail Substances**} \\  & & & & & & **Standards** & **Guidelines** & **Standards, Polish** & **Standards** & **Origin** & **Discharged to** \\  & & & & & & **US EPA [62] & **WHO [73] & **Ministry of Health [74]** & **Category A3 [75]** & **Runf [76]** \\ \hline Bacteria & CPU/mL & 500 & 124,000 & 22,761 & nd & nd & 100 & nd & nd & nd \\ Fungi & CPU/mL & 0 & 3000 & 498 & nd & nd & nd & nd & nd \\ pH & 6.3 & 7.6 & 6.8 & 6.5-8.5 & nd & 6.5-9.5 & 5.5-9.0 & 6.5-9.0 \\ EC & \(\mu\)S/cm & 8.8 & 58.8 & 26.1 & nd & nd & 2500 & 1000 & nd \\ CT & mg/L & \(<\)LQO & 5.56 & 1.72 & 250 & nd & 250 & 250 & 1000 \\ N-NO\({}_{3}\) & mg/L & \(<\)LQO & 0.748 & 0.277 & 10 & 50 & 50 & 50 & 30 \\ P-YO\({}_{4}\) & mg/L & \(\leq\)LQO & 0.014 & 0.237 & 0.045 & nd & nd & nd & nd \\ SO\({}_{4}\)\({}^{2}\) & mg/L & \(<\)LQO & 8.571 & 2.230 & 250 & nd & 250 & 250 & 500 \\ SO\({}_{2}\) & mg/L & \(\leq\)LQO & 0.752 & 0.418 & nd & nd & nd & nd & nd \\ Ag & mg/L & \(<\)LQO & 0.0761 & 0.0170 & 0.1 & 0.9 & 0.01 & nd & 0.1 \\ Al & mg/L & \(<\)LQO & 0.0412 & 0.0091 & 0.2 & nd & 0.2 & nd & 3 \\ Ba & mg/L & \(<\)LQO & 0.0168 & 0.0309 & 2 & 1.3 & nd & nd & 2 \\ Ca & mg/L & \(<\)LQO & 0.1726 & 2.0801 & 0.6096 & nd & nd & nd & nd & nd \\ Cu & mg/L & \(<\)LQO & 0.0199 & 0.0054 & 1 & 2 & 2 & 0.5 & 0.5 \\ K & mg/L & \(<\)LQO & 0.0867 & 1.0708 & 0.3649 & nd & nd & nd & nd & 80 \\ Mg & mg/L & \(<\)LQO & 0.0241 & 0.1175 & 0.0602 & nd & nd & 125 & nd & nd \\ Mo & mg/L & \(<\)LQO & 0.0307 & 0.0054 & 0.07 1 & 0.006 & nd & nd & 1 \\ Na & mg/L & \(<\)LQO & 0.4682 & 1.4067 & 0.7649 & 20 & nd & 200 & nd & 800 \\ Pb & mg/L & \(<\)LQO & 0.0058 & 0.0026 & nd & 0.01 & 0.01 & 0.05 & 0.5 \\ Sb & mg/L & \(<\)LQO & 0.0031 & 0.0008 & 0.006 & 0.02 & 0.005 & nd & 0.3 \\ Zn & mg/L & \(<\)LQO & 2.5786 & 0.6826 & 5 & nd & nd & 5 & 2 \\ \hline \hline \end{tabular}   
* CPU—The amounts of bacteria and fungi in the Krakow city roof runoff varied both in terms of season and sampling sites, but no distinct patterns were identified, although bacteria were clearly more abundant (Table 1, Table S5). The mean value of the bacteria content was the lowest during the spring of 2019 (3140 CFU/mL) and the highest in the winter of 2020 (47,590 CFU/mL), while in case of fungi, the mean value was the lowest in the autumn of 2019 (105 CFU/mL) and the highest in the winter of 2020 (1090 CFU/mL). The data did not correspond to those obtained in reference site (MOG--Figure 1, Table S5), where the highest amounts of both bacteria and fungi were detected during autumn 2019, and the lowest ones in spring 2019 (in case of bacteria) or in winter 2020 (in case of fungi). All these emphasized the absence of any trend in term of microbiological contamination of roof runoff. As the composition of roof runoff reflects the composition of the air, those two could be expected to be consistent. The unpublished data from 2018 on the microbiological contamination of the air in Krakow and two other nearby, smaller towns (Oswiecim and Brzesko) showed that the amounts of airborne microorganisms were also highly variable throughout the year, without a distinct pattern.