The effect of ash, water vapor, and heterogeneous chemistry on the evolution of a Pinatubo-size volcanic cloud

Abstract

Abstract. We employ the ECHAM5/MESSy2 atmospheric chemistry general circulation model (EMAC) that incorporates calculations of gas-phase and heterogeneous chemistry coupled with the ozone cycle and aerosol formation, transport, and microphysics to calculate the 1991 Pinatubo volcanic cloud. We considered simultaneous injections of SO2, volcanic ash, and water vapor. We conducted multiple ensemble simulations with different injection configurations to test the evolution of SO2, SO42-, ash masses, stratospheric aerosol optical depth, surface area density (SAD), and the stratospheric temperature response against available observations. We found that the volcanic cloud evolution is sensitive to the altitude where volcanic debris is initially injected and the initial concentrations of the eruption products that affect radiative heating and lofting of the volcanic cloud. The numerical experiments with the injection of 12 Mt SO2, 75 Mt of volcanic ash, and 150 Mt of water vapor at 20 km show the best agreement with the observation aerosol optical depth and stratospheric temperature response. Volcanic water injected by eruptive jet and/or intruding through the tropopause accelerates SO2 oxidation. But the mass of volcanic water retained in the stratosphere is controlled by the stratospheric temperature at the injection level. For example, if volcanic materials are released in the cold point above the tropical tropopause, most of the injected water freezes and sediments as ice crystals. The water vapor directly injected into the volcanic cloud increases the SO42- mass and stratospheric aerosol optical depth by about 5 %. The coarse ash comprises 98 % of the ash injected mass. It sediments within a few days, but aged submicron ash could stay in the stratosphere for a few months providing SAD for heterogeneous chemistry. The presence of ash accelerates the SO2 oxidation by 10 %–20 % due to heterogeneous chemistry, radiative heating, lofting, and faster dispersion of volcanic debris. Ash aging affects its lifetime and optical properties, almost doubling the ash radiative heating. The 2.5-year simulations show that the stratospheric temperature anomalies forced by radiative heating of volcanic debris in our experiments with the 20 km injection height agree well with observations and reanalysis data. This indicates that the model captures the long-term evolution and climate effect of the Pinatubo volcanic cloud. The volcanic cloud's initial lofting, facilitated by ash particles' radiative heating, controls the oxidation rate of SO2. Ash accelerates the formation of the sulfate layer in the first 2 months after the eruption. We also found that the interactive calculations of OH and heterogeneous chemistry increase the volcanic cloud sensitivity to water vapor and ash injections. All those factors must be accounted for in modeling the impact of large-scale volcanic injections on climate and stratospheric chemistry.

Interactive Stratospheric Aerosol Microphysics‐Chemistry Simulations of the 1991 Pinatubo Volcanic Aerosols With Newly Coupled Sectional Aerosol and Stratosphere‐Troposphere Chemistry Modules in the NASA GEOS Chemistry‐Climate Model (CCM)

“…(2020) also reported in a simulation of Kelut that SO 2 may undergo heterogeneous reactions on ash while Abdelkader et al. (2023) suggest that injected water vapor can enhance stratospheric OH. Such effects are not included in our simulations, but they might have resulted in a loss of SO 2 more rapid than in our simulations.…”

“…Further work is necessary to quantify the magnitude of this effect in smaller eruptions in the satellite record or in larger historical eruptions, like in Clyne et al (2021). Zhu et al (2020) also reported in a simulation of Kelut that SO 2 may undergo heterogeneous reactions on ash while Abdelkader et al (2023) suggest that injected water vapor can enhance stratospheric OH. Such effects are not included in our simulations, but they might have resulted in a loss of SO 2 more rapid than in our simulations.…”

Dispersion and Aging of Volcanic Aerosols After the La Soufrière Eruption in April 2021

“…The results of Abdelkader et al. (2023) revealed a doubling of the radiative effect in the SW and LW when considering ash aging in climate simulations of Pinatubo‐size eruptions. Zhu et al.…”

“…Their simulations showed that the volcanic cloud rises by 1 km/day during the first week, primarily due to the ash-induced heating and lofting. The results of Abdelkader et al (2023) revealed a doubling of the radiative effect in the SW and LW when considering ash aging in climate simulations of Pinatubo-size eruptions. Zhu et al (2020) showed that the ash particles controlled the chemistry and optical properties of volcanic clouds in the first days to weeks after the Mt.…”

Inverse Modeling of the Initial Stage of the 1991 Pinatubo Volcanic Cloud Accounting for Radiative Feedback of Volcanic Ash

“…The long‐term evolution of stratospheric volcanic clouds is sensitive to the height of emissions. The vertical distribution of volcanic material shapes the intense dynamic, chemical, and microphysical processes in a volcanic cloud (Abdelkader et al., 2022; Stenchikov, 2021). The satellite observations available at the time of the Mt.…”