The Antarctic ozone depletion caused by Erebus volcano gas emissions

Accepted Manuscript The Antarctic ozone depletion caused by Erebus volcano gas emissions V.V. Zuev, N.E. Zueva, E.S. Savelieva, V.V. Gerasimov PII:

S1352-2310(15)30424-6

DOI:

10.1016/j.atmosenv.2015.10.005

Reference:

AEA 14163

To appear in:

Atmospheric Environment

Received Date: 4 June 2015 Revised Date:

1 October 2015

Accepted Date: 2 October 2015

Please cite this article as: Zuev, V.V., Zueva, N.E., Savelieva, E.S., Gerasimov, V.V., The Antarctic ozone depletion caused by Erebus volcano gas emissions, Atmospheric Environment (2015), doi: 10.1016/j.atmosenv.2015.10.005. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT 1

The Antarctic ozone depletion caused by Erebus volcano gas emissions

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V. V. Zuev a, b, c, N. E. Zueva a, E. S. Savelieva a, *, V. V. Gerasimov a, b

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a

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E-mail address: [email protected] (V. V. Zuev), [email protected] (N. E. Zueva), [email protected] (V. V. Gerasimov)

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Institute of Monitoring of Climatic and Ecological Systems of the Siberian Branch of the Russian Academy of Sciences, 10/3, Academichesky ave., 634055, Tomsk, Russia b National Research Tomsk State University, 36, Lenina ave., 634050, Tomsk, Russia c National Research Tomsk Polytechnic University, 30, Lenina ave., 634050, Tomsk, Russia * Corresponding author. E-mail address: [email protected] (E. Savelieva). Telephone: (3822) 492–448.

Heterogeneous chemical reactions releasing photochemically active molecular chlorine play a key role in Antarctic stratospheric ozone destruction, resulting in the Antarctic ozone hole. Hydrogen chloride (HCl) is one of the principal components in these reactions on the surfaces of polar stratospheric clouds (PSCs). PSCs form during polar nights at extremely low temperatures (lower than –78 °C) mainly on sulfuric acid (H2SO4) aerosols, acting as condensation nuclei and formed from sulfur dioxide (SO2). However, the cause of HCl and H2SO4 high concentrations in the Antarctic stratosphere, leading to considerable springtime ozone depletion, is still not clear. Based on the NCEP/NCAR reanalysis data over the last 35 years and by using the NOAA HYSPLIT trajectory model, we show that Erebus volcano gas emissions (including HCl and SO2) can reach the Antarctic stratosphere via high-latitude cyclones with the annual average probability P ann. of at least ~ 0.235 (23.5%). Depending on Erebus activity, this corresponds to additional annual stratospheric HCl mass of 1.0 to 14.3 kilotons (kt) and SO2 mass of 1.4 to 19.7 kt. Thus, Erebus volcano is the natural and powerful source of additional stratospheric HCl and SO2, and hence, the cause of the Antarctic ozone depletion, together with man-made chlorofluorocarbons.

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Keywords: springtime ozone depletion, Erebus volcano, polar vortex, high-latitude cyclones, hydrogen chloride, sulfur dioxide.

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Abbreviations: VCD, vertical column density; PSCs, polar stratospheric clouds; CFCs, chlorofluorocarbons; UVB, ultraviolet B; DU, Dobson units; HCl, hydrogen chloride; Cl2, molecular chlorine; Cl, chlorine atoms; ClO, chlorine monoxide radicals; ClONO2, chlorine nitrate; SO2, sulfur dioxide; H2SO4, sulfuric acid aerosols.

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1. Introduction

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The ozone layer is known to absorb the bulk of solar ultraviolet B (UVB) rays, i.e. only a

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small part of UVB reaches the Earth's surface, and therefore, it protects Earth's biological systems

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from this dangerous radiation (Stolarski et al., 1992; Zerefos et al., 1997). However, this layer is

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depleted due to various reasons, especially over Antarctica. Based on ozone observations in 1982 at

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Syowa station (69°00′ S, 39°35′ E) in Antarctica, Chubachi (1984) revealed the smallest value of

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total ozone since 1966. Soon after, based on the Halley Bay station (75°35′ S, 26°34′ W) data,

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Farman et al. (1985) revealed a smooth decrease since 1972 and a considerable depletion in the

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early 1980's in the total ozone also over Antarctica. The ozone depletion was attributed to man-

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made chlorofluorocarbons (CFCs) and the region, wherein the total ozone value is less than 220

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Dobson Units (DU), was called later the “ozone hole”. For more than twenty years the springtime

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ozone hole area has exceeded 20 million km2 and spread over biologically-rich Antarctic waters. As

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a consequence, enhanced solar UVB radiation adversely affects Antarctic marine ecosystems and

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leads to a reduction in bioresources (diatoms, phytoplankton, etc.) (Smith et al., 1992; Kondratyev

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and Varotsos, 1996, 2000; Karentz and Bosch, 2001). Solomon et al. (1986) proposed the key chemical processes and catalytic cycles describing the

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Antarctic springtime ozone depletion. Heterogeneous reactions, occurring on the surfaces of polar

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stratospheric clouds (PSCs) of both types I and II (Rex et al., 1998; Finlayson-Pitts and Pitts, 2000)

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and releasing photochemically active molecular chlorine (Cl2), play a key role in these processes.

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PSCs form during winter-spring periods in Antarctica at extremely low stratospheric temperatures

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(lower than –78 °C) on sulfuric acid (H2SO4) aerosols, acting as condensation nuclei and formed

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from sulfur dioxide (SO2) (Solomon et al., 2005; Finlayson-Pitts and Pitts, 2000). The release of Cl2

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occurs mainly in the reactions of chlorine nitrate (ClONO2) with hydrogen chloride (HCl) (Solomon

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et al., 1986; Solomon, 1999):

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PSC

ClONO 2 + HCl → Cl2 + HNO3 ,

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or

(1)

PSC

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ClONO 2 + H 2 O → HOCl + HNO3 ,

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HOCl + HCl → Cl2 + H 2 O .

(2)

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PSC

(3)

Subsequently, the Cl2 is photolyzed into two chlorine atoms (Cl) by weak solar radiation Cl 2 + hν (250 < λ < 470 nm) → 2Cl ,

(4)

where hν = hc λ is the photon energy required to break a chemical bond, λ is the wavelength, and

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h and c are the Planck constant and speed of light, respectively. Ozone molecules are destroyed by

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Cl in the catalytic reaction:

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Cl + O3 → ClO + O 2 .

(5)

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Generally, ozone holes appear over Antarctica in springtime due to the following factors: 1) winter-

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spring formation of a stable polar vortex, which isolates the Antarctic stratosphere and cools it to

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extremely low temperatures (lower than –78 °C); 2) PSCs formation on condensation nuclei (H2SO4

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aerosols) at these temperatures; and 3) ozone destruction in reactions (1)–(5) (Finlayson-Pitts and

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Pitts, 2000; Newman, 2010).

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CFCs are assumed to be the main source of inert chlorine reservoir molecules HCl and

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ClONO2. After entering the equatorial (tropical) stratosphere, the CFCs are photolyzed by UV

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radiation, releasing Cl (Newman, 2010). In the middle and upper stratosphere, Cl atoms are

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converted into HCl via Cl + CH 4 → HCl + CH 3 ,

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(6)

and chlorine monoxide (ClO) radicals produced in reaction (5) are converted into ClONO2 via M

ClO + NO 2 → ClONO 2 ,

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where M is a third body (Newman, 2010). These HCl and ClONO2 molecules are then transported

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to both the Arctic and Antarctic polar stratospheres via the Brewer-Dobson circulation.

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(7)

However, we revealed that HCl vertical column density (VCD) over the Arrival Heights

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station in Antarctica is considerably higher than that observed over other Earth’s regions including

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Arctic one, whereas ClONO2 is distributed homogeneously enough in the Earth’s stratosphere.

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Moreover, we also revealed that concentration of H2SO4 aerosols formed from SO2 is higher in the

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Antarctic stratosphere in comparison with that in the Arctic one (see section 3.1). These facts

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cannot be explained by only the Brewer-Dobson circulation and are indicative of an effective source

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of HCl and SO2 within the Antarctic continent. Thus, the aims of the present work are: 1) to identify

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the source of HCl and SO2 in Antarctica; 2) to determine the delivery mechanisms of HCl and SO2

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from the source to the Antarctic stratosphere; and 3) to estimate the amount of additional annual

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HCl and SO2 masses reaching the stratosphere.

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2. Data and methods

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We used the following databases in this study. The information on the global distribution of

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the vertical column densities of HCl and ClONO2 over different stations, as well as on the aerosol

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backscattering coefficients over both the Arctic and Antarctic stations, is contained in the NOAA's

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National Weather Service Network for the Detection of Atmospheric Composition Change

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(NDACC, http://www.ndsc.ncep.noaa.gov) online database. The total ozone data over Halley Bay

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station used in this study were taken from the World Ozone and Ultraviolet Data Center (WOUDC,

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http://www/woudc.org). The border of the ozone hole in 2014 and the ozone hole area (1979–2014)

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were

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http://ozonewatch.gsfc.nasa.gov/SH.html) data. To determine the air-mass forward trajectories, we

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used the HYSPLIT-compatible NOAA meteorological data from GDAS (Global Data Assimilation

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System) half-degree archive. The geopotential heights of constant pressure surfaces were retrieved

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from National Centers for Environmental Prediction / National Center for Atmospheric Research

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(NCEP/NCAR,

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reanalysis data (Kalnay et al., 1996).

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determined

based

on

the

NASA's

Goddard

Space

Flight

Center

http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.html) 3

(GSFC,

global

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All the air-mass forward trajectories started from the summit of Mount Erebus were

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calculated by using the NOAA's Hybrid Single-Particle Lagrangian Integrated Trajectory

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(HYSPLIT) model (Draxler and Hess, 1998, http://ready.arl.noaa.gov/HYSPLIT.php).

3. Results

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3.1. HCl and SO2 source identification

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The VCDs of HCl and ClONO2 correspond to their values in the stratosphere due to the

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following reasons. First, ClONO2-producing reaction (7) is not effective due to the very low amount

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of ClO molecules in the troposphere. Second, HCl is removed rather rapidly from the troposphere

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by wet scavenging (Marcy et al., 2004). Note that the gas-phase HCl is hydrophilic, and hence, has

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a low lifetime in the troposphere. The monthly average VCD values of HCl and ClONO2 over four

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middle- and high-latitude stations in both the Northern and Southern Hemispheres are presented in

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Fig. 1. ClONO2 is seen in Fig. 1 to be rather homogeneously distributed in the Earth’s stratosphere,

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whereas the VCD of HCl over the Arrival Heights station in Antarctica is about 1.5–2 times higher

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than that over other Earth’s regions including the Arctic one.

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Fig. 1. The monthly average VCD values of HCl and ClONO2 over different stations. The HCl minimum values in both polar regions are caused by HCl adsorption on PSCs during winter-spring periods. There is no information on the VCD values for nighttime periods.

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ACCEPTED MANUSCRIPT In addition to the high VCD of HCl, a higher concentration of aerosols is also observed in the

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Antarctic stratosphere in comparison with that in the Arctic one. Fig. 2 shows the vertical profiles

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of aerosol backscattering coefficients, retrieved from NDACC lidar data for the wavelength

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λ = 532 nm over the McMurdo station (77°51′ S, 166°40′ E) in Antarctica and the Ny-Alesund

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station (78°55′ N, 11°55′ E) in the Arctic. The profiles are averaged over March–April period (for

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Antarctica) and November (for the Arctic region) of 2001 and 2002. Since PSCs do not form in the

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polar stratosphere at relatively high temperatures during these months, the retrieved aerosol profiles

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mainly represent H2SO4 aerosol ones. As seen from Fig. 2, the stratospheric H2SO4 aerosol

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concentration over Antarctica was higher than that over the Arctic, even after an explosive eruption

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occurred on May 22, 2001 at Shiveluch volcano (56°39′ N, 161°22′ E, elevation 3307 m), whose

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eruption column reached an absolute height of 20 km and increased the aerosol concentration

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(GVP, 2001).

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Fig. 2. Vertical profiles of aerosol backscattering coefficients averaged over March–April period (for the McMurdo station) and November (for the Ny-Alesund station) of 2001 and 2002.

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These facts (presented in Figs. 1 and 2) lead us to a conclusion that there should be a powerful

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and permanent additional source of volcanic nature for HCl and SO2 within the Antarctic continent.

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Note that the high stratospheric H2SO4 aerosol concentration is usually related to oxidation of SO2

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erupted into the stratosphere by volcanoes (Finlayson-Pitts and Pitts, 2000).

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Erebus volcano (77°32′ S, 167°09′ E, summit elevation 3794 m) located on Ross Island, Ross

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Sea, is known to be the only burning volcano in Antarctica and one of the most active volcanoes on

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the Earth. The volcanic activity restarted in 1972 and is ongoing at the present time. At the

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beginning of the 1980s, the activity was extremely high, and therefore, degassing volumes were 5

ACCEPTED MANUSCRIPT considerably higher compared to the present-day ones (Rose et al., 1985; Kyle et al., 1994; Zreda-

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Gostynska et al., 1993). Erebus volcano is noted for its persistent and permanent gas and aerosol

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emissions mostly occurring via lava lake degassing (Oppenheimer and Kyle, 2008). The

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predominant components of Erebus volcano gas emissions are H2O, CO2, CO, SO2, HF and HCl

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(Oppenheimer and Kyle, 2008). Note that Erebus gas emissions have high HCl/SO2 mass ratio of

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0.28 to 0.92 (Zreda-Gostynska et al., 1993; Oppenheimer and Kyle, 2008; Wardell et al., 2008), one

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of the highest in the world (Boichu et al., 2011).

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Erebus volcano eruptions are of the Strombolian type, which volcanic ejecta and gases are

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known to reach heights of 1–2 km above the volcano summit and, therefore, cannot directly reach

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the stratosphere (Boichu et al., 2010; Boichu et al., 2011; Dibble et al., 2008). However, according

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to aircraft observations in 1989 at a height of 8 km over Antarctica, the detected aerosol particles

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were identified as volcanic ejecta of Erebus (Chuan, 1994). Together with HCl and H2SO4 high

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concentrations in the Antarctic stratosphere, it is indicative of delivery mechanisms of Erebus

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volcanic gases into the Antarctic stratosphere.

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3.2. Delivery mechanisms of Erebus volcano gas emissions into the stratosphere

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Erebus volcano gas emissions can ascend to the Antarctic stratosphere via high-latitude

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cyclones which are coupled to the stratospheric polar vortex in cold seasons. Here and elsewhere we

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consider only those high-latitude cyclones whose ascending air flows are able to transport air

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masses from at least Erebus summit elevation (3794 m) to the Antarctic stratosphere. Long-term

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meteorological observations showed that there is usually a large-scale anticyclone in the lower

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troposphere over the Antarctic continent during March to October, whereas high-latitude cyclones

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dominate over the Antarctic coastline (Simmonds and Keay, 2000). Due to the asymmetry of the

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Antarctic continent relative to the geographic pole, the cyclones, moving along the west coast with

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meridional component of velocity, penetrate deep into the western Antarctic seas, including the

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Ross Sea (Simmonds et al., 2003). Owing to permanent passive and explosive degassing of Erebus

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volcano (Aster et al., 2003; Oppenheimer et al., 2011; Jones et al., 2008), its gas emissions with

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high probability (see section 3.3) can enter, and be transported into the stratosphere by, the

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ascending air flows during March to October. The air-mass forward trajectory calculated by NOAA

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HYSPLIT model with starting time at 00:00 UTC 30 May 2014 and ending time at 21:00 UTC 26

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August 2014, and using the NOAA GDAS data, is shown in Fig. 3 as an example. The trajectory

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started from the summit of Mount Erebus. One can see that the bulk of the trajectory is within the

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ozone hole area formed in September 2014, according to the GSFC data. To calculate the trajectory

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we used the vertical motion method (option “remap mean sea level to above ground level”), as

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recommended by the model developers for areas with sparse network of meteorological stations like 6

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ACCEPTED MANUSCRIPT Antarctica. The vertical slice of the trajectory is shown in the bottom of Fig. 3. Air masses

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(including Erebus volcanic gases) reached the Antarctic lower stratosphere (about 9–10 km) and an

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absolute height of 22 km in approximately 6 days and two months, respectively. Due to the polar

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vortex, the vortex motion of air masses provides adequate mixing of volcanic gases in the region of

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ozone depletion.

Fig. 3. Air-mass forward trajectory from NOAA HYSPLIT model with starting time at 00:00 UTC 30 May 2014 and ending time at 21:00 UTC 26 August 2014. The trajectory started from the summit of Mount Erebus (black five-point star). The black dashed line denotes the border of the ozone hole formed in September 2014.

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The location of the high-latitude cyclones can be determined by using the geopotential heights

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of constant pressure surfaces. Based on the NCEP/NCAR global reanalysis data for 30 May 2014,

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the 1000, 850, 700, 600, 250, 100 and 50 hPa geopotential height fields (corresponding to 0, 1.5, 3,

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4, 10.5, 16, and 20.5 km) over Antarctica are shown in Figs. 4a and 4b. The geopotential height

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distribution in Fig. 4a shows a pressure pattern typical for winter months over the Antarctic region.

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Namely, a polar anticyclone occurs over the continent, whereas a cyclone core is directly over the

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Ross Sea. With increase of height the cyclone gradually extends, and then spreads over the whole

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continent beginning from the height of Erebus summit (about 4 km). The cyclone, started in fact

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from the Ross Sea surface (Fig. 4a), is discernible throughout the troposphere up to the lower

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stratosphere (Fig. 4b), where it is coupled to, and embeds in, the polar vortex. The air-mass forward

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ACCEPTED MANUSCRIPT trajectory, the same as in Fig. 3, is shown in three dimensions in Fig. 4c. The trajectory reflects a

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quick ascent of Erebus volcanic gases to the stratosphere within the high-latitude cyclone and their

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thorough mixing inside the polar vortex at heights between 14 and 22 km. Thus, the presence of

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high-latitude cyclones directly over the Ross Sea provides the ascent of Erebus volcano gas

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emissions to the Antarctic stratosphere.

a

b

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c Fig. 4. 1000, 850, 700, and 600 hPa geopotential height fields corresponding to 0, 1.5, 3, and 4 km (a); 600, 250, 100, and 50 hPa geopotential height fields corresponding to 4, 10.5, 16, and 20.5 km (b); air-mass forward trajectory, the same as in Fig. 3, shown in three dimensions (c). The isolines are given in increments of 0.2 km. The normal line passes through the Mount Erebus coordinates.

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ACCEPTED MANUSCRIPT 3.3. Additional annual stratospheric HCl and SO2 masses

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To estimate the amount of HCl and SO2 masses transported annually to the Antarctic

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stratosphere by high-latitude cyclones, we analyzed the 600 and 250 hPa geopotential height fields

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corresponding to the height of the Erebus summit (∼ 4 km) and the lower stratosphere (∼ 10.5 km)

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using the NCEP/NCAR reanalysis daily data. The analysis showed that high-latitude cyclones were

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over the Ross Island during 118.8 days per year on average for the last 35 years (1980 to 2014), i.e.

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the annual average probability P ann.

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0.325 (or 32.5 %). In April to September period the average probability P Ap.-to-Sep. increases to 0.49,

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whereas from July to August the average probability P Jul.-to-Aug. goes up to 0.58.

Ross Is.

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of a high-latitude cyclone to be over the Ross Island equals Ross Is.

SC

Ross Is.

High-latitude cyclones, as well as middle-latitude ones, are known to be asymmetric and,

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therefore, have ascending air flows in their front sides and central parts, and descending ones in

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their back sides. To estimate the probability of Erebus gas emissions to ascend to the stratosphere

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via a high-latitude cyclone located over the Ross Island, we calculated the air-mass forward

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trajectories started from the summit of Mount Erebus using NOAA GDAS data over the whole

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2014 year and the NOAA HYSPLIT model. Note that, as the NOAA GDAS data are available only

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since July 2013, we chose the data of 2014 to be analyzed. The trajectory analysis, made for all the

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cyclones observed over the Ross Island during 2014, showed that the annual average probability

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P ann.

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During April to September the average probability P Ap.-to-Sep. increases to 0.757, whereas from July

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to August the average probability P Jul.-to-Aug. goes up to 0.767. Hence, we obtain for the annual

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average probability of Erebus volcano gas emissions to reach the Antarctic stratosphere:

Ant. strat.

of air masses to ascend to the stratosphere via such a cyclone equals 0.722 (or 72.2 %).

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Ross Is.

P ann. = P ann.

Ant. strat.

× P ann.

= 0.325 × 0.722 = 0.235 ,

(8)

or 23.5 %. For the April to September and July to August periods the corresponding probabilities

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Ant. strat.

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Ross Is.

Ant. strat.

Ross Is.

Ant. strat.

P Ap.-to-Sep. = P Ap.-to-Sep. × P Ap.-to-Sep. ,

(9)

P Jul.-to-Aug. = P Jul.-to-Aug. × P Jul.-to-Aug. ,

(10)

equal 0.371 and 0.445.

HCl

SO2

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According to various measurement data, the masses of HCl and SO2 (i.e. M ann. and M ann. )

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emitted annually by Erebus volcano vary from 4.1 to 60.9 kilotons (kt) and from 6.0 to 83.9 kt,

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respectively (see Table 1 in Supplementary Material). Taking into account the annual average

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probability P ann. = 0.235 calculated using Eq. (8), we obtain that the annual HCl and SO2 masses

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(i.e. m ann. and m ann. ), reaching the Antarctic stratosphere via high-latitude cyclones 9

HCl

SO 2

ACCEPTED MANUSCRIPT HCl

HCl

SO 2

SO 2

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m ann. = M ann. × P ann. ,

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m ann. = M ann. × P ann. ,

(11) (12)

vary from 1.0 to 14.3 kt and from 1.4 to 19.7 kt, respectively, depending on Erebus volcanic

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activity. The estimated probabilities, and hence, the HCl and SO2 masses entered the stratosphere

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have their least values, because the calculations were made on the assumption that all the volcanic

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gas emissions are concentrated near the Erebus summit crater. However, Erebus volcanic ejecta and

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gases can often reach the heights of more than 1 km above its summit (Boichu et al., 2010; Boichu

249

et al., 2011; Dibble et al., 2008). As high-latitude cyclones extend with height increase (Fig. 4a,b),

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the probability of the volcanic gases to enter the cyclones and then be transported into the

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stratosphere can essentially increase. Note that the Erebus gas emissions were maximal during the

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volcano anomalous activity in the early 1980s.

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4. Discussion

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The Erebus volcanic activity restarted in 1972. Until the early 1980s, gas emission rate

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measurements from Erebus volcano were performed only in January 1978 and showed relatively

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low rate values (e.g. the SO2 emission rate was of 0.95 kt/year) (Polian and Lambert, 1979).

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However, the measurements performed in November 1980 (Radke, 1982) indicated anomalously

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high volcanic activity of Erebus, when the SO2 emission rate was of 69.38 ± 36.58 kt/year.

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Furthermore, the emission rate reached a value of 83.88 ± 32.80 kt/year in 1983 (Rose et al., 1985).

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It should be noted that in the early 1980s, the extremely high Erebus activity was synchronous with

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intensive ozone depletion, detected over the Halley Bay station (Farman et al., 1985), and an

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increase of the springtime ozone hole area.

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Let us consider the time dependence of the September average total ozone over the Halley

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Bay station (WOUDC data) and the ozone hole area (GSFC data), which are shown in Fig. 5. One

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can see that the springtime total ozone content has decreased by 60 DU in ten years and dropped

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below the ozone hole level (220 DU) in the early 1980s. Since 1992 to the present day, the

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September total ozone content is seen in Fig. 5 to remain low (164 ± 15 DU) with the exception in

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September 2002, when the sudden stratospheric warming resulted in the smaller ozone hole size and

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the ozone hole split (Varotsos, 2002). The Antarctic stratosphere was warmed by strong, large-scale

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weather systems originated in the mid-latitude troposphere in late September (Varotsos, 2004a,b;

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Mohanakumar, 2008). As a consequence of this warming, PSCs were destroyed and ozone

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penetrated the Antarctic stratosphere from lower latitudes. It led to an increase in the total ozone

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content and a decrease in the ozone hole area. The high total ozone value and the corresponding low

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ozone hole area are marked in Fig. 5 by the triangles as anomalous.

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ACCEPTED MANUSCRIPT In Fig. 5, the annual average HCl and SO2 emission rates, based on various measurement data

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(Table 1 in Supplementary Material), are also given for comparison. Unfortunately, these data are

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very fragmentary, especially for HCl. Nevertheless, the available data allow for the conclusion that

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the annual average HCl and SO2 emission rates are uniquely associated to the September

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(springtime) total ozone content. The extremely high Erebus volcano gas emissions (including HCl

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and SO2) in the early 1980s not only stimulated ozone depletion and ozone hole formation, but also

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resulted in the subsequent total ozone decrease due to accumulation of volcanic gases in the

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Antarctic stratosphere. In addition, the Erebus stable volcanic activity in the following years was

283

the cause, to some extent, of low values of the springtime total ozone up to the present time.

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Fig. 5. Time dependence of the September average total ozone over the Halley Bay station and the ozone hole area alone with annual average HCl and SO2 emission rates (the 1–σ uncertainties are given for SO2). The triangles denote anomalously high total ozone value and the ozone hole area in 2002.

5. Conclusion

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In this study, we revealed that Erebus volcano is the powerful and permanent source of

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additional amount of HCl and SO2 gases in the Antarctic stratosphere. Both HCl, being one of the

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principal components in heterogeneous reactions on PSCs, and SO2, forming H2SO4 aerosols acting

292

as condensation nuclei for PSCs, play a significant role in the Antarctic springtime ozone depletion.

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Volcanic gases (including HCl and SO2), emitted by Erebus via its lava lake degassing, ascend to

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and penetrate the polar vortex, and hence, the Antarctic stratosphere via high-latitude cyclones over

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the Ross Sea. The annual average probability of the cyclone to be over the Ross Sea (Island) is

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0.325. The annual average probability of Erebus volcano gas emissions to ascend to the stratosphere

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via the cyclone is 0.722. Therefore, the annual average probability of HCl and SO2 gases to reach 11

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the Antarctic stratosphere equals 0.235. This probability corresponds to additional annual

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stratospheric HCl mass of 1.0 to 14.3 kt and SO2 mass of 1.4 to 19.7 kt, depending on Erebus

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activity. Thus, for more than 40 years, Erebus volcano, which activity restarted in 1972, has been a

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natural source of chemical species destroying the Antarctic ozone. The extremely high Erebus

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volcanic activity in the early 1980s definitely made a major contribution to the increase of the ozone

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hole along with man-made chlorofluorocarbons. Regular observations of Erebus volcano gas

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emissions can help to predict the total ozone content dynamics and, therefore, the ozone hole area.

Appendix A. Supplementary data

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See attached file

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Fig. 3. Air-mass forward trajectory from NOAA HYSPLIT model with starting time at 00:00 UTC 30 May 2014 and ending time at 21:00 UTC 26 August 2014. The trajectory started from the summit of Mount Erebus (black five-point star). The black dashed line denotes the border of the ozone hole formed in September 2014.

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Fig. 4. 1000, 850, 700, and 600 hPa geopotential height fields corresponding to 0, 1.5, 3, and 4 km (a); 600, 250, 100, and 50 hPa geopotential height fields corresponding to 4, 10.5, 16, and 20.5 km (b); air-mass forward trajectory, the same as in Fig. 3, shown in three dimensions (c). The isolines are given in increments of 0.2 km. The normal line passes through the Mount Erebus coordinates.

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Fig. 5. Time dependence of the September average total ozone over the Halley Bay station and the ozone hole area alone with annual average HCl and SO2 emission rates (the 1–σ uncertainties are given for SO2). The triangles denote anomalously high total ozone value and the ozone hole area in 2002.

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Highlights: Erebus volcanic gases reach the ozone layer via cyclones and the polar vortex. Annual HCl mass entering the stratosphere from Erebus varies from 1.0 to 14.3 kt. Annual SO2 mass entering the stratosphere from Erebus varies from 1.4 to 19.7 kt. HCl and SO2 emitted by Erebus volcano are a significant factor of ozone depletion. High Erebus activity in the early 1980s resulted in the ozone hole area increase.

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5. Supplementary information

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5.1 Collected data of SO2 and HCl emission rates

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Table 1. Annual average HCl and SO2 emission rates from Erebus volcano

Dec. 2004 Dec. 2005 Dec. 2006

0.95 Polian and Lambert, 1979 27.75 Radke, 1982 69.38±36.58 Harris et al., 1999 83.88±32.80 Rose et al., 1985 83.88±32.80* Kyle et al., 1994 9.14±3.78 Kyle et al., 1994 5.99±2.52 Kyle et al., 1994 7.57±4.10 Kyle et al., 1994 16.08±9.78 Kyle et al., 1994 9.78±3.15 Kyle et al., 1994 18.92±7.57 Kyle et al., 1994 25.86±7.25 Kyle et al., 1994 18.92±5.99 Sweeney et al., 2008 15.45±5.99 Sweeney et al., 2008 34.69±9.46 Sweeney et al., 2008 18.29 Wardell et al., 2004 14.19±6.31 Sweeney et al., 2008 16.71±8.51 Sweeney et al., 2008 20.81±6.62 Sweeney et al., 2008 19.87±5.36 Sweeney et al., 2008 30.91±9.15 Sweeney et al., 2008 27.12±6.31 Oppenheimer et al., 2005 27.12 Oppenheimer, Kyle, 2008 27.75±9.78 Sweeney et al., 2008 22.08±9.46 Boichu et al., 2011 17.03±5.36 Boichu et al., 2010

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60.86 Zreda-Gostynska et al., 1993 6.62 4.10 6.94 11.35 5.36 17.34 13.25

Zreda-Gostynska et al., 1993 Zreda-Gostynska et al., 1993 Zreda-Gostynska et al., 1993 Zreda-Gostynska et al., 1993 Zreda-Gostynska et al., 1993 Zreda-Gostynska et al., 1993 Zreda-Gostynska et al., 1993

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Oppenheimer, Kyle, 2008

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The emission rates given in Table 1 were calculated for the whole year, even though the

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emission rate measured during 2 to 5 days is assumed representative for the whole year (Kyle et al.,

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References

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Boichu, M., Oppenheimer, C., Roberts, T.J., Tsanev, V.I., Kyle, P.R., 2011. On bromine, nitrogen

11

oxides and ozone depletion in the tropospheric plume of Erebus volcano (Antarctica). Atmos.

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Environ. 45, 3856–3866. doi:10.1016/j.atmosenv.2011.03.027

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Boichu, M., Oppenheimer, C., Tsanev, V.I., Kyle, P.R., 2010. High temporal resolution SO2 flux

14

measurements at Erebus volcano, Antarctica. J. Volcanol. Geotherm. Res. 190, 325–336.

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doi:10.1016/j.jvolgeores.2009.11.020 Harris, A.J.L., Wright, R., Flynn, L.P., 1999. Remote monitoring of Mount Erebus volcano,

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Antarctica, using polar orbiters: Progress and prospects. Int. J. Remote Sens. 20, 3051–3071.

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Kyle, P.R., Sybeldon, L.M., McIntosh, W.C., Meeker, K., Symonds, R., 1994. Sulfur dioxide

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emission rates from Mount Erebus, Antarctica. In: Kyle, P.R. (Ed.), Volcanological and

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Environmental Studies of Mount Erebus, Antarctica, vol. 66. Antarctic Research Series, pp.

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Oppenheimer, C., Kyle, P.R., 2008. Probing the magma plumbing of Erebus volcano, Antarctica, by

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open-path FTIR spectroscopy of gas emissions. J. Volcanol. Geotherm. Res. 177, 743–754.

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doi:10.1016/j.jvolgeores.2007.08.022

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Oppenheimer, C., Kyle, P.R., Tsanev, V.I., McGonigle, A.J.S., Mather, T.A., Sweeney, D., 2005.

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Mt. Erebus, the largest point source of NO2 in Antarctica. Atmos. Environ. 39, 6000–6006.

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Polian, G., Lambert, G., 1979. Radon daughters and sulfur output from Erebus volcano, Antarctica.

Rose, W.I., Chuan, R.L., Kyle, P.R., 1985. Rate of sulphur dioxide emission from Erebus volcano, Antarctica, December 1983. Nature 316, 710–712. doi:10.1038/316710a0 Sweeney, D., Kyle, P.R., Oppenheimer, C., 2008. Sulfur dioxide emissions and degassing behavior Erebus

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from an alkaline intra-plate volcano: Mt. Erebus, Antarctica. J. Volcanol. Geoth. Res. 131,

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from Mount Erebus, Antarctica and estimated contributions to the Antarctic atmosphere.

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