## 3 Results and Discussion
[24] demonstrated that the main VOCs released from sour olive oils were hexanal, octane and acetic acid among other odorant compounds, which were identified as responsible for unpleasant odors when they exceeded their odor threshold concentration. Additionally, [PERSON] et al. [10] found that alperujo and orujo wastes generate VOCs, especially families of aldehydes and carboxylic acids when they are stored in open reservoirs in uncontrolled spaces. Moreover, the emissions' composition was influenced by the storage time and the environmental conditions. Figure 2 shows the distribution over time of the VOCs families considered in Table 3 throughout the six months of study. Alcohols, carboxylic acids and aldehydes were those families that presented the highest percentage of compounds corresponding to an average of 36%, 27% and 15%, respectively, for alperujo; and 41%, 21% and 10%, respectively, for orujo. In a previous study, [PERSON] et al. [10] determined that alcohols, carboxylic acids and aldehydes were also the predominant compounds in the emissions both from alperujo and orujo stored in open reservoirs due to a progressive decrease in the concentration of fatty acid methyl esters and alkenes in the emissions generated by biological and physical-chemical processes. Despite that most of the families showed no clear variability along the monitored period, still some families of VOCs showed a trend towards an increase or decrease over time. An increasing trend was observed for aliphatic and aromatic HCs in alperujo (Figure 2a) and for esters in orujo (Figure 2b). When results are analyzed based on the humidity of the samples (Table 1) and the rain precipitations (Table S1, supplementary material), there were no significant changes in the abundance of VOC families for the waste drying process. The endothermic drying of waste has the purpose of stabilizing the waste, reducing its weight and its volume, the latter as a consequence of water loss by evaporation by the addition of heat. In addition, [PERSON] et al. [25] have shown that water when evaporated transports most of the VOCs, which are released to the atmosphere. [PERSON] et al. (2019) described that VOCs have a wide range of evaporation temperatures. Most of them are evaporated at lower temperatures than water and their vaporization enthalpies are of the order of magnitude of water. Therefore, when water and VOCs are released from the waste in the form of vapor and contained within the mass of air circulating through the drying tremmel, they are removed from the system by depleting varying portions of the air mass charged with steam through the discharge and replacement of this exhaust air with equivalent amounts of fresh air containing less humidity. Tables 4 and 5 show the normal boiling temperatures of each of the key odorant compounds found, which are lower than the operating temperature in the dryer. Figure 2: Percentage distribution of VOCs by family in (**a**) alperujo and (**b**) orujo in the six-month experimentation period. In addition, Tables 4 and 5 show the quantification of VOCs that were considered as target compounds according to the results in Table 1. Concentrations were compared with the odor threshold concentrations also reported in Table 1.  
Except for furfural and 2-furanmethanol, concentrations of all target compounds exceeded their odor threshold in all samples analyzed in both alperujo and orujo. A comparison of the odor thresholds in Table 1 with the concentrations of odorants in Tables 4 and 5 show that for alperujo and orujo, the average benzaldehyde concentration exceeded its odor threshold by 25.7% and 14.3%, respectively. Similarly, acid acetic exceeded their odor threshold in alperujo and orujo by 81,666% and 86,666%, respectively. Hexanal, nonanal, octanal, phenol, hexane and toluene concentrations exceeded their odor thresholds in alperujo by 221%, 253%, 6,900%, 9,900%, 40% and 142% and 543%, 165%, 10,900%, 15,900%, 13.3% and 294% in orujo, respectively.