UV sensitivity to changes in ozone, aerosols, and clouds in Seoul, South Korea

The total ozone (O₃) and aerosol optical depth (AOD) at 320 nm have been observed from the ultraviolet (UV) measurements made at Yonsei University in Seoul, South Korea, with Dobson and Brewer spectrophotometers, respectively, during 2004-10. The daily datasets are analyzed to show the sensitivities of UV radiation to changes in O₃, AOD, and cloud cover (CC) together with global solar radiation (GS), including the long-term characteristics of surface UV irradiance in Seoul. The UV sensitivities show that 1% increases of O₃ and AOD relative to their reference values under all- and clear-sky conditions similarly manifest as 1-1.2% and 0.2% decreases of both daily erythemal UV (EUV) and total UV (TUV) irradiance at the ground level except for TUV sensitivity to O₃ (~0.3%). Those UV sensitivities to CC and GS changes are associated with a 0.12% decrease and 0.7% increase, respectively, in fractional UV changes. The trends show that the positive trends of O₃ (+7.2% decade^-1), AOD (+22.4% decade^-1), and CC (+52.4% decade^-1) induce negative trends in EUV (-8.4% decade^-1) and TUV (-2.5% decade^-1), in both UV (-4.7% decade^-1), and in EUV (-6.3% decade^-1) and TUV (-6.8% decade^-1), respectively. On the basis of the multiple linear regression analyses, it is found that UV sensitivity to O₃ is relatively high in the forcing factors, but the contributions of the UV forcing factors to the daily variability and the range of UV disturbances due to the variability of the forcing factors are affected more by AOD than by O₃ and CC in both UV fractional changes.