Dr. Valentina Aquila American University, Washington DC

Understanding the stratospheric aerosol layer: volcanic eruptions, pollution, and geoengineering

In the 1960’s, Christian Junge and his collaborators discovered a worldwide layer of predominantly sulfur aerosol at about 35 km altitude. This Junge aerosol layer, mainly originating by chemistry of carbonyl sulfide (OCS) and upwelling through the tropical tropopause, is often perturbed by volcanic eruptions that inject sulfur dioxide and sulfur aerosol in the stratosphere. This sudden perturbations can have dramatic impacts on the Earth’s climate, causing major perturbations of the Earth’s atmospheric composition and radiation balance. Additionally, relatively recent observations have identified a layer of enhanced aerosol extinction above the Asian Monsoon, hinting that tropospheric pollution can reach the stratosphere through convective systems. Given the scarcity of measurements, the uncertainty on the relative importance of these sources of stratospheric aerosol, as well as on its properties and composition, is still high. Reducing these uncertainties, however, is crucial now that the discussion about solar radiation management, i.e. the proposal of artificially increasing the Earth’s albedo through stratospheric aerosol to offset climate change, is moving outside of academia into the policy realm.  In this talk I will discuss the sources and impacts of stratospheric aerosol from volcanic eruptions, tropospheric pollution, and geoengineering, focusing on recent step forward and uncertainties that need to be addressed.