## 4 Discussion  
The focus of this study is reporting the malodorous VOCs in domestic cat urine and feces and the influence of aging urine and feces on the emitted VOCs. Domestic cats spray urine to mark their territory, and the odor is unpleasant to many people. The concentration of volatile compounds can differ by age and sex of the species [10]. This study reported several VOCs emitted from fresh cat urine and feces that were not reported in previous studies. The precursor of many sulfur-containing compounds, feline, was not identified previously in research [6]. As reported by [PERSON] et al. (2018), the presence of a fishy odor in the headspace of domestic cat anal sac secretions suggesting that cat urine can produce distinct fishy odorous trimethylamine is also present in our findings of the distinctive fishy odor in the fresh and stale feces but not in fresh or aged urine headspace [17]. In contrast, [PERSON] et al., 2020, reported the odor of trimethylamine released from a carpet contaminated with cat urine upon two weeks of aging; however, the \"fishy\" smell was absent in the emissions from fresh urine-treated carpets [18]. Feral male cats spray urine more often than females [19] and use unburied feces as scent-marking [20], and the released volatiles in both cases could be offensive to humans; the odor becomes even worse with time, although the VOC concentrations become trace levels in feces sample with time (Figure 4). This current study recorded the odor description of emitted VOCs that were never reported before for aged cat urine and feces studies. In addition to phenolics as a major odor contributor, indoles are prominent in stale urine, and organic acids and indoles are prominent in fresh urine odor. Our work supports that 2,5-dimethyl pyrazine and other pyrazines are the product of cat urine aging [11]. Additionally, this work also reports that longer (e.g., 50 min) exposure of the SPME to the aged urine headspace allowed the pyrazines, pyrrole, and pyrimidine to be absorbed onto the fiber and to be detectable in GC-MS. The use of SPME sampling has allowed easy preconcentrating of sample without the use of a solvent or derivatization of the VOCs responsible for the nuisance to human sensory organs. The volatile compound types and the relative PACs emitted by urine and feces significantly changed over time, even under laboratory conditions. The total number of compounds increased for the aged urine sample and decreased for the aged feces samples. Many esters and acidic VOCs dropped in number for the aged feces, either degraded to other compounds by the microbial community present in the sample, oxidized, or lost to the atmosphere during the aging process [11]. A number of phenol, alcohol, aldehyde, N-compounds (amines, pyrazines, and indoles), S-compounds (dimethyl disulfide and dimethyl sulfone), ketones, and acids reported in this study were emitted from the urine of lion, tiger, and domestic cat species as reported in previous studies (Table 4) [4,8,21]. Highly odorous gases emitted from urine or feces pose likely low inhalation risks. The human nose is very sensitive to many impactful odorants emitted from feces and urine in general. The nuisance odor experienced by homeowners or visitors can be attributed to stale urine. The aged urine is difficult to clean and completely remove from carpets and subflooring materials. Some homeowners experience these stale urine-like smells from floor areas that linger for years even after the cats are removed and no longer contributing urine. Once the carpet is contaminated with cat urine, many of the VOCs emitted are different compared to the VOCs emitted initially by urine itself; however, several VOCs emitted from the contaminated carpet are common to those reported here [18].