Effects of aerosols and water vapour on spatial-temporal variations of the clear-sky surface solar radiation in China

Clear-sky solar radiation is an important indicator describing the potential of solar energy. The aerosols and water vapour, apart from geometrical/astronomical ones, are the main factors resulting in the losses of the surface solar radiation (SSR) under clear sky conditions. This study uses satellite aerosol data, reanalysis water vapour data, and the Mesoscale Atmospheric Irradiance Code to create the clear-sky SSR dataset for China in 2001-2015. The aerosol direct radiative effect (ADRE) and water vapour radiative effect (WVRE) are calculated to study the clear-sky SSR losses due to aerosols and water vapour. The coefficient of determination (R-2) of the observations and simulations is 0.944. The mean absolute error (MAE) and root mean square error (RMSE) are 6.67% and 9.00%, respectively. The strongest attenuation in clear-sky SSR due to aerosols occurs in April in most areas of China, while in June in North China and the Yangtze River Delta, water vapour most strongly attenuates the clear-sky SSR in July, and the monthly solar radiation losses due to water vapour are higher than those due to aerosols. The high aerosol and water vapour contents are the reasons why the clear-sky SSR in North China and the Yangtze River Delta in June are lower than those in May. From 2001 to 2015, the clear-sky trend with the greatest increase of up to 0.389 W m(-2) per year (2.48% in 15 years) occurs over central Inner Mongolia, which is related to the reduction in dust. The increasing concentration of particulate matter in the atmosphere results in the most significant decreasing clear-sky trend in North China (-0.510 W m(-2) year(-1), 3.35% in 15 years). Generally, the ADRE variations are the main factor controlling the annual variations in clear-sky SSR.