Assessing the Influence of Aerosol on Radiation and Its Roles in Planetary Boundary Layer Development

A comprehensive measurement of planetary boundary layer (PBL) meteorology was conducted at 140 and 280 m on a meteorological tower in Beijing, China, to quantify the effect of aerosols on radiation and its role in PBL development. The measured variables included four-component radiation, temperature, sensible heat flux (SH), and turbulent kinetic energy (TKE) at 140 and 280 m, as well as PBL height (PBLH). In this work, a method was developed to quantitatively estimate the effect of aerosols on radiation based on the PBLH and radiation at the two heights (140 and 280 m). The results confirmed that the weakened downward shortwave radiation (DSR) on hazy days could be attributed predominantly to increased aerosols, while for longwave radiation, aerosols only accounted for around one-third of the enhanced downward longwave radiation. The DSR decreased by 55.2 W m(-2) on hazy days during noontime (1100-1400 local time). The weakened solar radiation decreased SH and TKE by enhancing atmospheric stability, and hence suppressed PBL development. Compared with clean days, the decreasing rates of DSR, SH, TKE, and PBLH were 11.4%, 33.6%, 73.8%, and 53.4%, respectively. These observations collectively suggest that aerosol radiative forcing on the PBL is exaggerated by a complex chain of interactions among thermodynamic, dynamic, and radiative processes. These findings shed new light on our understanding of the complex relationship between aerosol and the PBL.