Atmospheric visibility variation over global land surface during 1973–2012: Influence of meteorological factors and effect of aerosol, cloud on ABL evolution

Abstract

Atmospheric visibility (Vis) is used to evaluate air pollution over global land surface during 1973–2012. Over global more populated areas with major anthropogenic emissions and hygroscopic aerosol species, weaker surface wind is generally associated with more severe air pollution and Vis degradation, while an increase of relative humidity (RH) generally favors more efficient secondary formation and hygroscopic growth of aerosol and Vis impairment. The allocation of meteorological factor with the major aerosol component over global different areas can influence the formation and variation of aerosol and cloud, and their effects on the atmospheric boundary layer (ABL) evolution and air pollution. Over East Asia, India and Southeast Asia, the air pollution with a growing concern with Vis decrease can be associated to an increase in anthropogenic emission and a synchronous stabilization of ABL (characterized by a weakened, less variable surface wind and a decreased diurnal temperature range, DTR). Both the increase of aerosol loading and cloud cover could (i) increase daily minimum air temperature versus decrease daily maximum air temperature and result in a decrease of DTR, (ii) reduce solar radiation reaching the surface, stabilize the ABL and aggravate air pollution. While Vis increase over Europe could be related to more effective emission control and an intensification of surface wind. Also significantly, a close relationship is identified between RH and DTR; RH explains about 90% of the variance of DTR over Europe in summer; a drier weather is corresponding to a greater surface incoming short-wave flux and a greater DTR.