The Role of the Tropical West Pacific for Stratospheric Composition and Polar Ozone Loss
Hundreds of organic species are emitted into the atmosphere mostly from biogenic processes. The rapid breakdown by reactions with OH radicals prevents most of them from reaching the stratosphere. Hence, the omnipresent layer of OH in the troposphere shields the stratosphere from these emissions and is particularly relevant for those species that do not photolyse efficiently. Reactions involving ozone are a strong source of OH in clean tropical air. Hence the OH concentration is closely coupled to ozone abundances.
The Western Pacific warm pool is key for troposphere to stratosphere exchange. Ozone measurements from the center of the warm pool indicate ozone concentrations below the detection limit of the sondes throughout the troposphere. The uncertainties of ozonesonde measurements at these very low ozone concentrations, the robustness of the observations and the upper limit of the ozone concentration will be discussed. Tropospheric chemical transport modelling suggests the existence of a pronounced minimum in the tropospheric column of OH in the region of the tropical West Pacific ozone minimum.
This increases the lifetime of chemical species and has the potential to amplify the impact of surface emissions on the stratospheric composition. Specifically, the role of emissions of biogenic halogenated species from this geographic region for stratospheric ozone depletion will be shown. Also, the potential role of increasing anthropogenic emissions of SO2 in South East Asia or from minor volcanic eruptions for the stratospheric aerosol budget will be discussed.