Air pollution is pushing wind speed into a regulator of surface solar irradiance in China

Abstract

Analysis in 27 cities across China shows that surface solar irradiance (SSI) and wind speed track similar decadal trends in 1961–2011, suggesting wind speed as a possible regulator of SSI. This assumption is further confirmed by the continuously widening gap in annually averaged daily SSI between windy and windless clear-sky days with worsening air pollution. Wider gaps are noted for more polluted cities and seasons. The gap in SSI between windy and windless conditions could therefore serve as a good indicator for air quality. The regulatory effect of wind speed on SSI starts to be important when air pollution index exceeds the boundary of 125. A plausible mechanism of wind speed regulating SSI through interactions with aerosols is proposed. There are two cut-off points of 2.5 m s ^−1 and 3.5 m s ^−1 wind speeds. Winds <2.5 m s ^−1 noticeably disperse air pollutants and thereby enhance SSI. Above the 2.5 m s ^−1 threshold, air pollution and SSI become largely insensitive to changing wind speeds. Winds in excess of 3.5 m s ^−1 could enhance aerosol concentration probably by inducing dust-storms, which in turn attenuate SSI.