![[Plot of stratospheric Aerosol Optical Depth vs Time]](Image1.gif)
The Effect of Large Volcanic Eruptions on Arctic Ozone Loss and Recovery
Research Staff: Azadeh Tabazadeh and Katja Drdla
Eruptions with a volcanic explosively index (VEI) of 4 or higher produce significant stratospheric injections. Sulfur dioxide, the most important atmospheric component of volcanic emissions, is converted into sulfate aerosols after injection into the stratosphere. More than one hundred eruptions with VEIs equal to or greater than 4 are thought to have occurred in the past 500 years. In Figure 1, the historical record of volcanic eruptions is inferred from the aerosol optical depth measurements. However, only about half of all large eruptions are sulfur-rich. Both the 1982 El Chichon (VEI = 4) and 1991 Mt. Pinatubo (VEI = 5) eruptions were sulfur-rich, producing volcanic clouds in the stratosphere which lasted for a number of years. In Figure 2, the time evolution of the Pinatubo volcanic plume is shown 1 day, 1 month and 2 months after the eruption. It is clear that volcanic aerosols are abundant in the Arctic region within a few months after the eruption. On the other hand, the relatively sulfur-poor eruption of Mt. St. Helens (VEI = 5) in 1980 contributed very little sulfate mass to the stratospheric aerosol layer. Overall, large sulfate-rich eruptions are common. Therefore it is important to understand to what extent they could affect the Arctic ozone layer in the next 30 years or so
while anthropogenic chlorine levels are still sufficiently high (~3 ppbv) to cause severe ozone depletion.Model simulations have shown that the early rapid growth of the Antarctic "ozone hole" in the early 1980s may have been influenced in part by a number of large volcanic eruptions. The goal of this study is to explore how a large eruption could affect Arctic ozone loss processes, such as chlorine activation and denitrification, in a cold year within the current range of natural variability. It is projected that the Arctic climate may be colder in the future as a result of greenhouse gas emissions and their built-up in the lower troposphere. Thus, we also investigate how a possible large eruption could affect ozone loss in a colder Arctic climate. In this project we use a chemistry-microphysics model (the IMPACT model) to investigate how the continuous presence of volcanic cloudy-like conditions in the Arctic can affect ozone loss processes, such as chlorine activation and denitrification, in a cold year such as the winter of 1999-2000.
Point of Contact: Azadeh Tabazadeh, 650/604-1096, atabazadeh@mail.arc.nasa.gov
![[Picture of Dispersal of Mt Pinatubo Plume]](tabazadeh-fig2.gif)