Fig. 1. Extinction characteristics of sunlight in atmosphere

Fig. 2. Action spectrum of solar erythemal UV radiation

Fig. 3. Solar UV spectra observed in Lhasa at local noon for two equinoxes and two solstices

Fig. 4. Monochromatic solar erythemal ultraviolet intensity versus wavelength in Lhasa at local noon for two equinoxes and two solstices

Fig. 5. Observation devices. (a) NILU-UV solar UV detector; (b) RAMSES-ACC-UV UV spectrometer

Fig. 6. Number of clear days per month at three regions of Tibet

Fig. 7. Diurnal variation characteristics of solar erythemal UV radiation on clear days in 2017 at Tingri. (a) January—June; (b) July—December

Fig. 8. Diurnal variation characteristics of solar erythemal UV radiation on clear days in 2014 in Lhasa. (a) January—June; (b) July—December

Fig. 9. Diurnal variation characteristics of solar erythemal UV radiation on clear days in 2018 at Nyingchi. (a) January—June; (b) July—December

Fig. 10. Deviation of solar erythemal UV peak intensity. (a) Dose rate of solar erythemal UV radiation on February 8, 2014 in Lhasa; (b) dose rate of solar erythemal UV radiation versus solar zenith angle on February 8, 2014 in Lhasa

Fig. 11. Daily maximum dose rates of solar erythemal UV radiation on clear days at three regions of Tibet

Fig. 12. Daily total dose rates of solar erythemal UV radiation on clear days at three regions of Tibet