2.4.2. Heavy metal analysis Before sampling, the filters were washed with a mixture of hydrochloric acid, nitric acid, and distilled-deionizedwater to remove impurities. Subsequently, the filterswere rinsed again with distilledwater and were placed in an oven at 105 °C for 2 h. Afterwards, the filters were kept at a constant temperature of 18–20 °C and relative humidity of 40–50% for 24 h (Sowlat et al., 2013). After sampling, the second part of the 24-h measurement filter was put in a Teflon container for heavy metal analysis. Then, a mixture of nitric acid (2.5 mL), perchloric acid (1 mL), and hydrochloric acid (2.5 mL) was added into the container to digest the filter at 170 °C for 4 h. Subsequently, the Teflon container was placed on a heater at 95–100 °C to evaporate all remaining acid. The container was then cooled, concentrated nitric acid and distilled water were added, and it was shaken for 15 min. The obtained mixture was passed through a Whatman filter and then diluted to 10 mL with deionized water. The solution was stored in a plastic bottle at 4 °C until further analysis. The analysis of digested samples was carried out using ICPAES . The detection limits for the analyzed metals were as follows: As (0.179 μg·kg−1), Cd (0.049 μg·kg−1), Cr (0.096 μg·kg−1), Cu (0.306 μg·kg−1), Ni (0.28 μg·kg−1), Pb (2 μg·kg−1), V (0.5 μg·kg−1), Zn (0.3 μg·kg−1), Fe (0.16 μg·kg−1), and Al (0.17 μg·kg−1)