Summer PM2.5 concentrations in the northern subtropics modulated by the Hadley circulation edge location

Atmospheric aerosols play a pivotal role in impacting the global energy budget and public health. Meteorological conditions significantly affect PM2.5 concentrations at regional scales, while the potential influence of circulation on PM2.5 concentrations in the entire latitude belt from a hemispheric scale remains unknown. Here, we focused on the impact of interannual variations of northern Hadley circulation (HC) edge (NHCE) on PM2.5 concentrations variations during boreal summer on the hemispheric scale. We determined that a northward (southward) shift in the NHCE leads to increased (decreased) PM2.5 concentrations over the northern subtropics within 20°–30°N, mainly through circulation processes. Variations in the latitude of the NHCE explain about 30% of the PM2.5 concentrations averaged over 20°–30°N, with the strongest impacts over North Africa, where NHCE-regulated anomalies of local PM2.5 concentrations reach 36%. The northwards shift of NHCE is accompanied by an overall migration of the northern cell of HC, corresponding to anomalous rising as well as divergence (convergence) in the upper (lower) troposphere over northern subtropics, resulting in enhanced PM2.5 concentrations. Our results are verified by numerical model with fixed anthropogenic emissions. Besides, the amplitude of poleward HC over the past four decades is comparable to the interannual NHCE variation, indicating that the risk of increased PM2.5 concentrations over the northern subtropics may increase. This study highlights the significant modulation of interannual variation of NHCE latitude on PM2.5 concentrations, implying that the effects of circulation may be essential for environmental policy formulation in the northern subtropics.