Contribution of stratospheric intrusion to tropospheric hydroxyl radical

Abstract. The hydroxyl radical (OH) is a key species that participates in many oxidation processes in the troposphere. Previous studies have reveal significant impact of lightning and air pollution on interannual variabilities and long-term trends of tropospheric OH. The abundance of OH in the troposphere is influenced by a multitude of factors, including ozone, water vapour, and ultraviolet radiation, among others. The tropospheric ozone is significantly influenced by the presence of stratospheric intrusion. It is hypothesized that the intrusion process will also exert an influence on tropospheric OH. In this study, the contribution of stratospheric intrusion to tropospheric OH is estimated through the use of a climate chemistry model. The findings suggest that the contribution of the stratosphere to tropospheric OH is most significant over the subtropical ocean regions (reaching 2×10⁻² ppt) and over the Tibetan Plateau in the summer (reaching 3×10⁻² ppt). The relative contribution of stratospheric intrusion can reach 12 % over the Tibetan Plateau, northern South America and South Africa, and 20 % over the subtropical oceans. It is expected that stratospheric contribution will increase in the future due to enhanced stratosphere troposphere exchange and stratospheric ozone recovery.