Impact of Air Pollution on Summer Surface Winds in Xi'an

By analysis of observation data, this paper demonstrates that pollution particles could reduce surface wind speed through blocking solar radiation to the ground. The comparation between temperature at the lowland meteorological station Xi'an and that over the nearby highland station Mt. Hua suggests that surface solar radiation at Xi'an is reduced due to the increasing anthropogenic aerosols. The reduced surface energy suppresses the atmospheric instability and convective flows, and thus the downward transfer of faster winds aloft is reduced. Consequently, wind speeds near surface are weakened. This reduction of surface winds is shown by the significant reverse trends of wind speeds over the two stations at different elevations. The aerosols' effects on winds are also manifested in the trends of radionsonde wind speed. The decreased surface winds in Xi'an have also reduced local pan evaporation.