The impact threshold of the aerosol radiative forcing on the boundary layer structure in the pollution region

Recently, there has been increasing interest in the relation between particulate matter (PM) pollution and atmospheric-boundary-layer (ABL) structure. This study aimed to qualitatively assess the interaction between PM and ABL structure in essence and further quantitatively estimate aerosol radiative forcing (ARF) effects on the ABL structure. Multi-period comparative analysis indicated that the key to determining whether haze outbreak or dissipation occurs is whether the ABL structure satisfies the relevant conditions. However, the ABL structure change was in turn highly related to the PM level and ARF. |SFC−ATM| (SFC and ATM are the ARFs at the surface and interior of the atmospheric column, respectively) is the absolute difference between ground and atmosphere layer ARFs, and the |SFC−ATM| change is linearly related to the PM concentrations. However, the influence of ARF on the boundary layer structure is nonlinear. With increasing |SFC−ATM|, the turbulence kinetic energy (TKE) level exponentially decreased, which was notable in the lower layers or ABL, but disappeared at high altitudes or above the ABL. Moreover, the ARF effects threshold on the ABL structure was determined for the first time, namely once |SFC−ATM| exceeded ∼55 W m−2, the ABL structure tends to quickly stabilize and thereafter change little with increasing ARF. The threshold of the ARF effects on the boundary layer structure could provide useful information for relevant atmospheric-environment improvement measures and policies, such as formulating phased air pollution control objectives.