Atmospheric planetary boundary layer (PBL), also called atmospheric boundary layer, is the region of the lower troposphere where Earth’s surface strongly influences temperature, moisture, and wind through the turbulent transfer of air mass. The PBL controls the dispersion of air pollutants and is closely related with the human life. The interaction between aerosol (air pollutants) and PBL has attracted much attention in recent years owing to its critical role in the formation of haze episodes in China. Previous studies have shown that the positive feedback of aerosol and PBL is an important factor in the haze episodes. However, what the role of different types of aerosol (scattering and absorption) is in the development of PBL remains unclear.

"We found the aerosol acts sometimes as a stove, a dome and even an umbrella on the PBL, depending on its optical properties and altitudes." Said Prof. XIN Jinyuan with the Institute of Atmospheric Physics at the Chinese Academy of Sciences.

In a recently published study in Geophysical Research Letters, Prof. XIN and Prof. Scot T. MARTIN of Harvard University constructed the model of aerosol stove, dome and umbrella effects using a large-eddy simulation model incorporated with the observations of a typical stagnant weather day.

"PBL comprises of a bottom-up structure of a near-surface stable boundary layer (SBL), a residual layer (RL), and a capping inversion layer (CIL) during the nighttime, and a convection boundary layer (CBL) and a CIL during the daytime." Said XIN, "We found that the increase of absorption aerosol concentration below RL strongly heats the lower atmosphere, induces the entrainment, and promotes the PBL development. We call it aerosol stove effect."

 
For the absorption aerosol layer above RL, according to the study, the increase of aerosol concentration that traps more solar radiation strongly heats the temperature inversion layer. This strengthens the inversion intensity and exhibits a strong inhibition on PBL. This is called dome effect since it acts as a lid to impede the development of PBL.

Figure 1. Schematic description of aerosol-PBL interactions with absorption aerosol layer below RL, absorption aerosol layer above RL, purely scattering aerosol layer below RL, and purely scattering aerosol layer above RL. (Image by XIN Jinyuan) 

In the cases of purely scattering aerosol, the suppression of PBL depends on aerosol loading rather than the height of aerosol layer so the aerosol is like an umbrella that reflects the solar radiation back to the out space.

Results reveal that there exists a transition height, above which absorption aerosol dominates the suppression of PBL (dome effect > aloft umbrella effect) and below which the purely scattering aerosol is more important (surface umbrella effect > stove effect). This transition height is highly related to the RL height.

The results provide scientific references for the pollution control strategies. It is necessary to strictly control the burning activities which produce a large amount of absorption pollutants (e.g., black carbon and brown carbon) in the upwind area in the south of North China Plain (NCP) to avoid the dome effect. For the local NCP, measures such as vehicle restriction and desulfurization of coal burning should be specially strengthened to reduce the emission of scattering aerosol and its gaseous precursors (e.g., sulfur dioxide and nitric oxide) in order to eliminate the surface umbrella effect.

Schematic diagram for the application of the aerosol stove, dome, and umbrella effect during NCP hazy events. (a) Southerly transport scenario of NCP region. (b) Haze formation process interpreted by "double inhibitions". (Image by XIN Jinyuan)

Citation：
Yongjing Ma; Jianhuai Ye; Jinyuan Xin*; Wenyu Zhang; Vilà-Guerau de Arellano Jordi; Shigong Wang; Dandan Zhao; Lindong Dai; Yongxiang Ma; Xiaoyan Wu; Xiangao Xia; Guiqian Tang; Yuesi Wang; Pengke Shen; Yali Lei; and Scot T. Martin* (2020). The Stove, Dome, and Umbrella Effects of Atmospheric Aerosol on the Development of the Planetary Boundary Layer in Hazy Region. Geophysical Research Letters, 47, e2020GL087373. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL087373.

Media contact: Ms. LIN Zheng, jennylin@mail.iap.ac.cn