As shown in Figure 4, the values of Baseline 1, determined initially, are quite stable and the range is between 15 and 20 ppb. The following monitoring was carried out during printing, with filtering system. Compared to baseline it is evident an increase of ozone’s concentration. After a few minutes, a measure of ozone shows a return of the values to initial concentrations (Baseline 2). It was done a measure during a second printing, without filtering system. The results are clearly in evidence: the values of ozone increased significantly, reaching values