Science Seminars

The Impact of Volcanic Eruptions on Stratospheric Chemistry and Aerosols

Speaker: Yunqian Zhu (LASP and NCAR)
Date: Thursday, Apr 29, 2021
Time: 4:00 pm
Location: zoom

Seminar Abstract:

Volcanic eruptions release gases (e.g., H2O, CO2, SO2, H2S, HCl) and solid matter into the atmosphere. Volcanic particles can affect the climate by scattering solar radiation. In addition, stratospheric chemistry can change because of heterogeneous reactions on volcanic particles. Increased stratospheric aerosols due to numerous small eruptions since 2002 have been observed by various in-situ and remote platforms. Here, we present two studies of the impact of small eruptions on stratospheric sulfur chemistry, ozone chemistry, and aerosol burdens.

We investigate the impact of the 2015 Mount Calbuco eruption and previous eruptions on stratospheric aerosols, polar stratospheric clouds, and ozone depletion. The simulated volcanic sulfate aerosol from the Mount Calbuco eruption penetrated the Antarctic vortex in May 2015 and thereafter. Volcanic sulfate aerosol from Mount Calbuco and previous eruptions caused the ozone hole to develop earlier in the year and to have a larger area.

Volcanic ash is often neglected in climate simulations because ash particles are assumed to have a short atmospheric lifetime, and to not participate in sulfur chemistry. After the Mt. Kelut eruption in 2014, stratospheric ash-rich aerosols were observed for months. Here we show that the persistence of super-micron ash is consistent with a density near 0.5 g cm−3, close to pumice. Ash-rich particles dominate the volcanic cloud optical properties for the first 60 days. We also find that the initial SO2 lifetime is determined by SO2 uptake on ash, rather than by reaction with OH as commonly assumed. About 43% more volcanic sulfur is removed from the stratosphere in two months with the SO2 heterogeneous chemistry on ash particles than without. This research suggests the need for re-evaluation of factors controlling SO2 lifetime in climate model simulations, and of the impact of volcanic ash on stratospheric chemistry and radiation.