Simulation of impact from stratospheric ozone on global tropospheric ozone distribution with a chemistry transport model: A case study during the 1990-1991 period

In this work we examine the effect of ozone (O-3) from the stratosphere on the O-3 levels in the troposphere. The tropopause is defined according to the potential vorticity (PV) and potential temperature distribution. Annual simulations were performed with and without stratospheric O-3 in the model to access the impact of stratospheric O-3 on tropospheric O-3 distribution. Our results show that surface O-3 over the tropical marine boundary layer is dominated by in-situ photochemistry in the troposphere. The maintenance of the inter-hemispheric asymmetry in ozone over the extra-tropical marine boundary layer is dominated by the transport of O-3 from the stratosphere. Comparisons between the model and the surface measurements show that the model without stratospheric O-3 exhibits a hemispheric summer maximum, emphasizing the contributions of transport of O-3 and O-3 producing precursors from continental regions during the summer months, whilst no clear spring O-3 maximum is found. About 50%-80% of O-3 in the lower troposphere over the northern hemisphere mid-latitudes are photochemically produced during the northern hemisphere summer. About 20%-40% is due to tropospheric photochemistry in the lower troposphere during the northern hemisphere spring. We conclude that O-3 transported from the stratosphere is the dominating factor for the spring O-3 maximum over the extra-tropical latitudes, while the photochemical ozone production is the dominating factor for O-3 over the tropical marine boundary layer environments and over the land surface emission areas.