Urban impacts on mean and trend of surface incident solar radiation

Anthropogenic aerosols over urban areas may have important effects on surface incident solar radiation (R-s). Studies have claimed that R-s decreased significantly more in urban areas than in rural areas from 1964 to 1989. However, these estimates have substantial biases because they ignored the spatial inhomogeneity of R-s measurements. To address this issue, we selected urban-rural station pairs collocated within 2 degrees x 2 degrees and found 105 such pairs based on the Global Energy Balance Archive (GEBA). On average, the impact of urban aerosols on mean and trend of R-s is 0.2(0.7, median)+/-11.2W m(-2) and 0.1(-0.7, median)+/-6.6 W m(-2) per decade from 1961 to 1990, respectively. Hence, the averaged urban impacts on the mean and trend of R-s over Europe, China and Japan from 1961 to 1990 are small although they may be significant at specific sites.