Surface ozone over High-Mountain Asia controlled by stratospheric intrusion

Abstract. High-Mountain Asia (HMA) is a global hotspot of stratospheric intrusion, and elevated surface ozone were observed at ground monitoring sites. Still, links between the variability of surface ozone and stratospheric intrusion at regional scale remain unclear. This study synthesized ground measurements of surface ozone over the HMA and analyzed their seasonal variations. The monthly mean surface ozone concentrations peaked earlier in the south in April and later in the north in July over the HMA. The migration of monthly surface ozone peaks was coupled with the synchronous movement of tropopause folding and westerly jet that created a conducive conditions for stratospheric ozone intrusion. Such intrusion contributed ~65 % of surface ozone at three typical sites across the HMA. We demonstrated that surface ozone over the HMA is mainly controlled by stratospheric intrusion, which warrants a proper consideration in understanding atmospheric chemistry and impacts of ozone over this highland region and beyond.