## 3 Results and Discussion
[31] determined the content of trace elements (Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As and Pb) in aerosols generated during biomass combustion, under defined realistic combustion conditions, which included temperature changes and concentrations of O\({}_{2}\) and SO\({}_{2}\) in flue gas. Two different trends were observed: when O\({}_{2}\) was increased in the flue gas, the content of Cr, Ni and Mn increased, and the reverse effect was observed for the remaining elements. Changes in SO\({}_{2}\) concentration had little effect on the results, with the notable exception of Fe, the amount of which decreased with the increase of SO\({}_{2}\) in the flue gas. In samples taken at two different temperatures (566 \({}^{\circ}\)C and 900 \({}^{\circ}\)C), at higher temperatures Pb and Cu in the gas phase were found, while Cr, Mn, Fe, Ni and Zn were condensed earlier. Pb was condensed between 560 \({}^{\circ}\)C and 900 \({}^{\circ}\)C, while part of Cu was not condensed and was still present as a lower temperature vapor. According to the authors of [30], among the operation factors (temperature, heating rate, reaction time, etc. ), temperature is the main factor in the redistribution of heavy metals. Moisture and Cl content are important, especially in high temperature thermal processes (combustion and gasification), because the authors found that the moisture content reduces the volatility of heavy metals, while the content of Cl causes them to volatilize. Thermally stable metals (Cr, Mn and Ni) are less volatile under typical conditions in the temperature range of 200-1100 \({}^{\circ}\)C during thermal processes and they are contained in residues. On the contrary, heavy metals with lower thermal stability (Hg, Cd, As and Pb) are susceptible to volatility. The content of heavy metals in biomass ash presented in [32] was generally below the limits for fertilizers or soils. However, the significant variability in mineral and chemical composition of ash indicates that a comprehensive examination of ash samples is necessary to determine the possible scope of its application. To investigate the effect of biomass and combustion temperature on the content of each of the analyzed elements in the ash samples, a two-way analysis of variance (two-way ANOVA) was carried out. The test results are summarized in Table 1.  
Based on the obtained results (Table 1), a significant impact of biomass, temperature and biomass and temperature interaction on the content of individual metals in ash was found (all _p_-values \(<\) 0.001). The Tukey test examined detailed differences between means and determined homogeneous groups of average contents of individual trace elements in the biomass under study (Table 2). The average content of Cr, Cu, Fe, Ni and Zn for the raw materials tested differed significantly at the significance level of 0.05 (Table 2). For Cd, no significant differences were found between pine and willow. There was no significant difference in mean Pb content for miscant and willow. As to temperature comparisons (Table 3), the Tukey test found significant differences for all the means comparisons at the significance level of 0.05. The detailed differences between the means were also examined when considering the combination of biomass and temperature (Table 4). In the columns corresponding to the examined elements, the means that did not differ significantly are marked with the same letters. Different groups of