## 3 Results and Discussion
As can be seen, an increase in the ESR signal was observed immediately after UV exposure (solid red line). The increase of the signal following UV exposure was about 1-2 orders of magnitude higher than the initial signal before UV exposure (solid gray line). Differences in the maximum UV-induced signals (main singlet) can also be noticed among the five sample sets, which may be due to the intra-sample variability in the fingernails' sensitivity to UV. The fading characteristics of the UV-induced signal also appeared to be variable among different storage and location conditions. Another important finding following UV exposure was the appearance of the \"bulge\" in the spectra (between g = 2.014 and 2.024), which was described as the resulting effect of the fingernails' exposure to high-heating temperatures [3]. This unexpected presence of the \"bulge\" may be due to the temperature change during the UV exposure process. To determine the reason behind this unexpected result, we recorded the temperature and humidity in real time during the UV exposure process with the use of three different dual channel data loggers. The dual data channel loggers were placed under the UV light for 30 min for five consecutive times (this is similar to the procedure conducted during exposure of the samples to UV). The results are shown in Figure 6. Here one can see the gradual changes in the temperature and humidity with UV exposure time. The temperature and humidity continuously increased and decreased, respectively, until the UV exposure time stopped. These changes in the temperature and humidity during UV exposure showed qualitatively the same behavior, as seen in Figure 6. The average maximum recorded temperature was 50 \({}^{\circ}\)C, and the average minimum recorded humidity was 8%. The increase in the temperature, which occurred continuously during UV exposure, was the reason for the apparent appearance of the \"bulge\" [3]. While the \"bulge\" was reportedly observed mostly in high-heating temperatures (i.e., beyond >80 \({}^{\circ}\)C), it may be possible that the UV exposure contributed to the exacerbation of its occurrence. Lastly, it should also be noted that the stability of the \"bulge\" behaved in a similar fashion as the UV-induced signal (main singlet) under the same storage and location conditions. In other words, the vacuum storage at LT with no light exposure was able to keep both the \"bulge\" (assuming this is a by-product of the heat-related induced signal) and UV-induced signal intact up to 7 days (compared to the non-vacuum storage at RT with light exposure), as illustrated in Figure 5.  
Figure 5: Time evolution of the ESR spectra in unirradiated and untreated samples following UV exposure for 30 min, as described in step 1 of Experiment 2. Each sample set was stored under different storage and location conditions. Each spectrum or datum point was obtained as the average of four subsets. The notations RT, LT, w/light, and w/o light are the same as in Figure 4.  
Figure 7, on the other hand, shows the comparison of the peak-to-peak intensities obtained from five different sample sets stored under various storage conditions, as described in steps 1-4 of Experiment 2. Plotted values from AAT1 (i.e., starting from step 2) were calculated as the average of three AAT samples and subtracted from the (background) control sample. Note that the plotted peak-to-peak intensity values for the UV exposure (i.e., step 1) were obtained from the \"main singlet\" of the spectra only. The UV-induced signals recorded from both vacuum- and non-vacuum-stored samples at RT with no light exposure were observed to have constant fading (up to 7 days) compared to the samples with light exposure. The sample sets with light exposure exhibited similar fading during the first few days (up to 3 days) followed by a subsequent signal increased at 7 days post-measurement. In contrast, a slower fading behavior of the UV-induced signal was observed in vacuum-stored samples at LT with no light exposure.