## 4 Results and Discussion
### Emissions of CO, NOx and SO\({}_{2}\)  
Analyses of carbon monoxide (CO) emissions have indicated high emissions of this gas during the combustion of oil pressing residues. The highest value at 5712.3 g kg\({}^{-1}\) among the analyzed cakes was recorded for flax residues, while the lowest value was recorded for milk thistle residues (2523 g kg\({}^{-1}\)). Biochar materials, on the other hand, were characterized by significantly lower carbon monoxide emissions. Each time, the lowest values were recorded for pyrolysates obtained at the maximum parameters of the pyrolysis process. Analyzing all the biochars obtained, the emission levels during their combustion were approximated in the range of 35.33-2821.67 g kg\({}^{-1}\). The lowest value characterized the pyrolysates obtained from fennel flower cakes. The content of nitrogen oxides in the cakes subjected to combustion was in the range of 78.96-116.33 g kg\({}^{-1}\). The highest emission value was recorded during the combustion of evening primrose seed residues, while the lowest was recorded for rapeseed cake. In the case of the pyrolysates obtained, inconclusive results regarding nitrogen oxide emissions during their combustion were obtained. In the case of cakes from fennel flower, rapeseed, evening primrose and milk thistle, significantly lower values were recorded than in the control sample. In turn, the pyrolysates obtained from flax and hemp had higher NOx emissions than the control samples. The lowest NOx emissions were determined in the case of the combustion of pyrolysates of fennel flower, with an average value of 17.14 g kg\({}^{-1}\) and a minimum value of 2.67 g kg\({}^{-1}\). Subjecting the obtained cakes to the combustion process made it possible to determine the emission of sulfur dioxide in the range of decreasing values, i.e., 291.33, 142.33, 123.32, 112.67, 87.66 and 94.31 g kg\({}^{-1}\) for rapeseed, hemp, fennel flower, evening primrose, flax and milk thistle, respectively. Pyrolys of cakes at 400 \({}^{\circ}\)C resulted in a several-fold decrease in SO\({}_{2}\) in the pyrolysates. Pyrolysates obtained at temperatures of 450 and 500 \({}^{\circ}\)C showed no sulfur dioxide emissivity in most of the variants analyzed. Only pyrolysates obtained from  
Figure 3: Calorific value of the tested cakes and biochars prepared from **(a)** fennel flower _(Nigella sativa L.)_, **(b)** rapeseed _(Brassica napus_ L. var. _Napus_), **(c)** flax _(Linum usitatissimum_ L.), **(d)** evening primrose _(Cenoptera biennis_ L.)_, **(e)** milk thistle _(Silbyum marianum_ L. _[PERSON]_)_, **(f)** hemp _(Cannabis sativa_ L.)_.  
rapeseed were found to emit SO\({}_{2}\) during their combustion. The values ranged from 103.67 (pyrolysates obtained at 400 \(\ {}^{\circ}\)C and in 5 min) to 13.65 g kg\({}^{-1}\) (pyrolysates obtained at 500 \(\ {}^{\circ}\)C and in 15 min) (Figure 4). According to [PERSON] et al. (2012), CO emissions during the combustion of firewood and crop residues were 47.8 and 52 g kg\({}^{-1}\), respectively. In contrast, the combustion of pine and corn pellets generated 4.4 and 17.9 g kg\({}^{-1}\) CO, respectively [74]. [PERSON] et al. (2021), in their study on the emission of carbon monoxide, total hydrocarbons and particulate matter during wood combustion in an operating store, report CO emissions in the range of 795.2 to 1983.1 ppm [75]. In contrast, in a study by [PERSON] et al. (2021) on the emission of carbon monoxide, total hydrocarbons and particulate matter during wood combustion in a stove operating under distinct conditions, CO emissions did not exceed 73.9 g kg\({}^{-1}\) for the materials analyzed, i.e., pine (_Pinus pinaster_) and beech (_Fagus sylvatica_) [76]. According to [PERSON] et al. (2023), biochar from grape pomace (pyrolysis in 350 \(\ {}^{\circ}\)C) heated to 900 \(\ {}^{\circ}\)C generates 2155 umol g\({}^{-1}\) CO. In contrast, an increase in the pyrolysis temperature (biochar 700 \(\ {}^{\circ}\)C) resulted in a decrease in emissions to a level of 1154 umol g\({}^{-1}\)[51]. According to [PERSON] et al.