Model simulations of the chemical and aerosol microphysical evolution of the Sarychev Peak 2009 eruption cloud compared   to in situ and satellite observations

Lurton, Thibaut; Jégou, Fabrice; Berthet, Gwenaël; Renard, Jean‐Baptiste; Clarisse, Lieven; Schmidt, Anja; Brogniez, Colette; Roberts, Tjarda

doi:10.5194/acp-18-3223-2018

Cited by 25 publications

(34 citation statements)

References 74 publications

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“…Although the instantaneous lifetime of SO 2 (with respect to oxidation by OH) is substantially increased in the halogen-free model plume, we note that the addition of halogen emissions to the model further suppresses OH, increasing the SO 2 lifetime and having a reductive effect on secondary aerosol production both in terms of mass and surface area ( Figure 7). This result for a tropospheric volcanic plume mirrors findings from a recent study of a stratospheric volcanic cloud (Lurton et al, 2018).…”

supporting

confidence: 87%

Observation and modelling of ozone-destructive halogen chemistry in a passive degassing volcanic plume

Surl¹,

Roberts²,

Bekki³

2021

Preprint

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Abstract. Volcanoes emit halogens into the atmosphere that undergo chemical cycling in plumes and cause destruction of ozone. The impacts of volcanic halogens are inherently difficult to measure at volcanoes, and the complexity of the chemistry, coupled with the mixing and dispersion of the plume, makes the system challenging to model numerically. We present aircraft observations of the Mount Etna plume in the summer of 2012, when the volcano was passively degassing. Measurements of SO2 – an indicator of plume intensity – and ozone were made in the plume a few 10s of km from the source, revealing a strong negative correlation between ozone and SO2 levels. From these observations we estimate a mean in-plume ozone loss rate of 1.3 × 10−5 molecules of O3 per second per molecule of SO2. This value is similar to observation-derived estimates reported very close to the Mount Etna vents, indicating continual ozone loss in the plume up to at least 10's km downwind. The chemically reactive plume is simulated using a new numerical 3D model WRF-Chem Volcano (WCV), a version of WRF-Chem we have modified to incorporate volcanic emissions (including HBr and HCl) and multi-phase halogen chemistry. We used nested grids to model the plume close to the volcano at 1 km. The focus is on the early evolution of passively degassing plumes aged less than one hour and up to 10's km downwind. The model reproduces the so-called bromine explosion: the daytime bromine activation process by which HBr in the plume is converted to other more reactive forms that continuously cycle in the plume. These forms include the radical BrO, a species whose ratio with SO2 is commonly measured in volcanic plumes as an indicator of halogen ozone-destroying chemistry. We track the modelled partitioning of bromine between its forms. The model yields in-plume BrO / SO2 ratios (around 10−4 mol/mol) similar to those observed previously in Etna plumes. The modelled BrO / SO2 is lower in plumes which are more dilute (e.g. at greater windspeed). It is also slightly lower in plumes in the middle of the day compared than in the morning and evening, due to BrO's reaction with diurnally varying HO2. Sensitivity simulations confirm the importance of near-vent products from high temperature chemistry, notably bromine radicals, in initiating the ambient temperature plume halogen cycling. Note also that heterogeneous reactions that activate bromine also activate a small fraction of the emitted chlorine; the resulting production of chlorine radical Cl causes a strong reduction in the methane lifetime and increasing formation of HCHO in the plume. Modelled rates of ozone depletion are found to be similar to those derived from aircraft observations. Ozone destruction in the model is controlled by the processes that recycle bromine, with about three-quarters of this recycling occurring via reactions between halogen oxide radicals. Through sensitivity simulations, a relationship between the magnitude of halogen emissions and ozone loss is established. Volcanic halogens cycling impacts profoundly the overall plume chemistry, notably hydrogen oxide radicals (HOx), nitrogen oxides (NOx), sulfur, and mercury chemistry. In the model, it depletes HOx within the plume, increasing the lifetime of SO2 and hence slowing sulfate aerosol formation. Halogen chemistry also promotes the conversion of NOx into nitric acid (HNO3). This, along with the displacement of nitrate out of background aerosols in the plume, results in enhance HNO3 levels and an almost total depletion of NOx in the plume. The halogen-mercury model scheme is simple but includes newly-identified photo-reductions of mercury halides. With this set-up, the mercury oxidation is found to be slow and in near-balance with the photo-reduction in the plume. Overall, the model findings demonstrate that halogen chemistry has to be considered for a complete understanding of sulfur, HOx, reactive nitrogen, and mercury chemistry, and of the formation of sulfate particles in volcanic plumes.

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supporting

confidence: 87%

Observation and modelling of ozone-destructive halogen chemistry in a passive degassing volcanic plume

Surl¹,

Roberts²,

Bekki³

2021

Preprint

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“…We use the UVSPEC (UltraViolet SPECtrum) radiative transfer model as implemented within the LibRadtran package (Mayer and Kylling, 2005) (http://www.libradtran.org/ doku.php, last access: 8 January 2021). With UVSPEC, the daily-average (equinox-equivalent) regional shortwave surface and top-of-the-atmosphere (TOA) radiative forcing (RF) are estimated.…”

Section: Uvspec Radiative Forcing Calculationsmentioning

confidence: 99%

Stratospheric aerosol layer perturbation caused by the 2019 Raikoke and Ulawun eruptions and their radiative forcing

et al. 2021

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Abstract. In June 2019 a stratospheric eruption occurred at Raikoke (48∘ N, 153∘ E). Satellite observations show the injection of ash and SO2 into the lower stratosphere and an early entrainment of the plume into a cyclone. Following the Raikoke eruption, stratospheric aerosol optical depth (sAOD) values increased in the whole Northern Hemisphere and tropics and remained enhanced for more than 1 year, with peak values at 0.040 (short-wavelength, high northern latitudes) to 0.025 (short-wavelength, Northern Hemisphere average). Discrepancies between observations and global model simulations indicate that ash may have influenced the extent and evolution of the sAOD. Top of the atmosphere radiative forcings are estimated at values between −0.3 and -0.4Wm-2 (clear-sky) and of −0.1 to -0.2Wm-2 (all-sky), comparable to what was estimated for the Sarychev eruption in 2009. Almost simultaneously two significantly smaller stratospheric eruptions occurred at Ulawun (5∘ S, 151∘ E) in June and August. Aerosol enhancements from the Ulawun eruptions mainly had an impact on the tropics and Southern Hemisphere. The Ulawun plume circled the Earth within 1 month in the tropics. Peak shorter-wavelength sAOD values at 0.01 are found in the tropics following the Ulawun eruptions and a radiative forcing not exceeding −0.15 (clear-sky) and −0.05 (all-sky). Compared to the Canadian fires (2017), Ambae eruption (2018), Ulawun (2019) and the Australian fires (2019/2020), the highest sAOD and radiative forcing values are found for the Raikoke eruption.

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“…1. As shown by Lurton et al (2018), volcanic halogens deplete the hydroxyl radical (OH) via Eq. (4),…”

Section: Sulfur Microphysics and Erf Arimentioning

confidence: 99%

“…It is clear, however, that volcanic halogens are injected into the stratosphere after some volcanic eruptions, but there is limited research into how these volcanic halogens may alter the volcanic aerosol microphysics, stratospheric chemistry, and volcanic forcing. Lurton et al (2018) simulated the 2009 Sarychev Peak eruption (0.9 Tg of SO 2 ) in CESM1(WACCM) (Community Earth System Model, Whole Atmosphere Community Climate Model) and showed how inclusion of co-emitted halogens (27 Gg of HCl) resulted in a lengthening of the SO 2 lifetime, due to the further depletion of OH, and a corresponding delay in the formation of aerosols, giving better agreement between modelled and observed SO 2 burden and showing how co-emitted halogens could impact volcanic sulfur processing. Tie and Brasseur (1995) utilised model calculations to show how background atmospheric chlorine loadings altered the ozone response to volcanic sulfur injections.…”

Section: Introductionmentioning

confidence: 99%

Co-emission of volcanic sulfur and halogens amplifies volcanic effective radiative forcing

et al. 2021

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Abstract. The evolution of volcanic sulfur and the resulting radiative forcing following explosive volcanic eruptions is well understood. Petrological evidence suggests that significant amounts of halogens may be co-emitted alongside sulfur in some explosive volcanic eruptions, and satellite evidence indicates that detectable amounts of these halogens may reach the stratosphere. In this study, we utilise an aerosol–chemistry–climate model to simulate stratospheric volcanic eruption emission scenarios of two sizes, both with and without co-emission of volcanic halogens, in order to understand how co-emitted halogens may alter the life cycle of volcanic sulfur, stratospheric chemistry, and the resulting radiative forcing. We simulate a large (10 Tg of SO2) and very large (56 Tg of SO2) sulfur-only eruption scenario and a corresponding large (10 Tg SO2, 1.5 Tg HCl, 0.0086 Tg HBr) and very large (56 Tg SO2, 15 Tg HCl, 0.086 Tg HBr) co-emission eruption scenario. The eruption scenarios simulated in this work are hypothetical, but they are comparable to Volcanic Explosivity Index (VEI) 6 (e.g. 1991 Mt Pinatubo) and VEI 7 (e.g. 1257 Mt Samalas) eruptions, representing 1-in-50–100-year and 1-in-500–1000-year events, respectively, with plausible amounts of co-emitted halogens based on satellite observations and volcanic plume modelling. We show that co-emission of volcanic halogens and sulfur into the stratosphere increases the volcanic effective radiative forcing (ERF) by 24 % and 30 % in large and very large co-emission scenarios compared to sulfur-only emission. This is caused by an increase in both the forcing from volcanic aerosol–radiation interactions (ERFari) and composition of the stratosphere (ERFclear,clean). Volcanic halogens catalyse the destruction of stratospheric ozone, which results in significant stratospheric cooling, offsetting the aerosol heating simulated in sulfur-only scenarios and resulting in net stratospheric cooling. The ozone-induced stratospheric cooling prevents aerosol self-lofting and keeps the volcanic aerosol lower in the stratosphere with a shorter lifetime. This results in reduced growth by condensation and coagulation and a smaller peak global-mean effective radius compared to sulfur-only simulations. The smaller effective radius found in both co-emission scenarios is closer to the peak scattering efficiency radius of sulfate aerosol, and thus co-emission of halogens results in larger peak global-mean ERFari (6 % and 8 %). Co-emission of volcanic halogens results in significant stratospheric ozone, methane, and water vapour reductions, resulting in significant increases in peak global-mean ERFclear,clean (> 100 %), predominantly due to ozone loss. The dramatic global-mean ozone depletion simulated in large (22 %) and very large (57 %) co-emission scenarios would result in very high levels of UV exposure on the Earth's surface, with important implications for society and the biosphere. This work shows for the first time that co-emission of plausible amounts of volcanic halogens can amplify the volcanic ERF in simulations of explosive eruptions. It highlights the need to include volcanic halogen emissions when simulating the climate impacts of past or future eruptions, as well as the necessity to maintain space-borne observations of stratospheric compounds to better constrain the stratospheric injection estimates of volcanic eruptions.

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Model simulations of the chemical and aerosol microphysical evolution of the Sarychev Peak 2009 eruption cloud compared to in situ and satellite observations

Cited by 25 publications

References 74 publications

Observation and modelling of ozone-destructive halogen chemistry in a passive degassing volcanic plume

Observation and modelling of ozone-destructive halogen chemistry in a passive degassing volcanic plume

Stratospheric aerosol layer perturbation caused by the 2019 Raikoke and Ulawun eruptions and their radiative forcing

Co-emission of volcanic sulfur and halogens amplifies volcanic effective radiative forcing

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