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

Abstract. Volcanoes emit halogens into the atmosphere that undergo complex chemical cycling in plumes and cause destruction of ozone. We present a case study of the Mount Etna plume in the summer of 2012, when the volcano was passively degassing, using aircraft observations and numerical simulations with a new 3D model “WRF-Chem Volcano” (WCV), incorporating volcanic emissions and multi-phase halogen chemistry. Measurements of SO2 – an indicator of plume intensity – and ozone were made in the plume a few tens of kilometres from Etna, revealing a strong negative correlation between ozone and SO2 levels. From these observations, using SO2 as a tracer species, 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-based estimates reported very close to Etna's vents, indicating continual ozone loss in the plume up to at least tens of kilometres downwind. The WCV model is run with nested grids to simulate the plume close to the volcano at 1 km resolution. The focus is on the early evolution of passively degassing plumes aged less than 1 h and up to tens of kilometres downwind. The model is able to reproduce the so-called “bromine explosion”: the daytime conversion of HBr into bromine radicals 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. The species BrO is produced in the ambient-temperature chemistry, with in-plume BrO / SO2 ratios on the order of 10−4 mol/mol, similar to those observed previously in Etna plumes. Wind speed and time of day are identified as non-linear controls on this ratio. Sensitivity simulations confirm the importance of near-vent radical products from high-temperature chemistry in initiating the ambient-temperature plume halogen cycling. Heterogeneous reactions that activate bromine also activate a small fraction of the emitted chlorine; the resulting production of chlorine radical Cl strongly enhances the methane oxidation and hence the formation of formaldehyde (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 halogen cycling profoundly impacts the overall plume chemistry in the model, 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 enhanced 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 of 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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Observation and modelling of ozone-destructive halogen chemistry in a passive degassing volcanic plume

10.5194/acp-2021-145 ◽

2021 ◽

Author(s):

Luke Surl ◽

Tjarda Roberts ◽

Slimane Bekki

Keyword(s):

Heterogeneous Reactions ◽

Mount Etna ◽

Volcanic Plume ◽

Activation Process ◽

Aerosol Formation ◽

Strong Negative Correlation ◽

Volcanic Plumes ◽

Ozone Loss ◽

Halogen Chemistry ◽

Aircraft Observations

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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Towards a representation of halogen chemistry within volcanic plumes in a chemistry transport model

Geoscientific Model Development Discussions ◽

10.5194/gmdd-7-2581-2014 ◽

2014 ◽

Vol 7 (2) ◽

pp. 2581-2650 ◽

Cited By ~ 4

Author(s):

L. Grellier ◽

V. Marécal ◽

B. Josse ◽

P. D. Hamer ◽

T. J. Roberts ◽

...

Keyword(s):

Transport Model ◽

Computational Cost ◽

Ambient Air ◽

Heterogeneous Reactions ◽

Tropospheric Chemistry ◽

Volcanic Plume ◽

Large Set ◽

Chemistry Transport Model ◽

Volcanic Plumes ◽

The Impact

Abstract. Volcanoes are a known source of halogens to the atmosphere. HBr volcanic emissions lead rapidly to the formation of BrO within volcanic plumes as shown by recent work based on observations and models. BrO, having a longer residence time in the atmosphere than HBr, is expected to have a significant impact on tropospheric chemistry, at least at the local and regional scales. The objective of this paper is to prepare a framework that will allow 3-D modelling of volcanic halogen emissions in order to determine their fate within the volcanic plume and then in the atmosphere at the regional and global scales. This work is based on a 1-D configuration of the chemistry transport model MOCAGE whose low computational cost allows us to perform a large set of sensitivity studies. This paper studies the Etna eruption on the 10 May 2008 that took place just before night time. Adaptations are made to MOCAGE to be able to produce the chemistry occurring within the volcanic plume. A simple sub-grid scale parameterization of the volcanic plume is implemented and tested. The use of this parameterization in a 0.5° × 0.5° configuration (typical regional resolution) has an influence on the partitioning between the various bromine compounds both during the eruption period and also during the night period immediately afterwards. During the day after the eruption, simulations both with and without parameterizations give very similar results that are consistent with the tropospheric column of BrO and SO2 in the volcanic plume derived from GOME-2 observations. Tests have been performed to evaluate the sensitivity of the results to the mixing between ambient air and the magmatic air at very high temperature at the crater vent that modifies the composition of the emission, and in particular the sulphate aerosol content that is key compound in the BrO production. Simulations show that the plume chemistry is not very sensitive to the assumptions used for the mixing parameter (relative quantity of ambient air mixed with magmatic air in the mixture) that is not well known. This is because there is no large change in the compounds limiting/favouring the BrO production in the plume. The impact of the model grid resolution is also tested in view of future 3-D-simulations at the global scale. A dilution of the emitted gases and aerosols is observed when using the typical global resolution (2°) as compared to a typical regional resolution (0.5°), as expected. Taking this into account, the results of the 2° resolution simulations are consistent with the GOME-2 observations. In general the simulations at 2° resolution are less efficient at producing BrO after the emission both with and without the subgrid-scale parameterization. The differences are mainly due to an interaction between concentration effects than stem from using a reduced volume in the 0.5° resolution combined with second order rate kinetics. The last series of tests were on the mean radius assumed for the sulphate aerosols that indirectly impacts the production of BrO by heterogeneous reactions. The simulations show that the BrO production is sensitive to this parameter with a stronger production when smaller aerosols are assumed. These results will be used to guide the implementation of volcanic halogen emissions in the 3-D configuration of MOCAGE.

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Quantification of the depletion of ozone in the plume of Mount Etna

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-23639-2014 ◽

2014 ◽

Vol 14 (16) ◽

pp. 23639-23680 ◽

Cited By ~ 1

Author(s):

L. Surl ◽

D. Donohoue ◽

A. Aiuppa ◽

N. Bobrowski ◽

R. von Glasow

Keyword(s):

Strong Dependence ◽

Source Region ◽

Mount Etna ◽

Volcanic Plumes ◽

Processing Times ◽

Atmospheric Processing ◽

Constant Rate ◽

Halogen Chemistry ◽

Reactive Halogen Species ◽

Halogen Species

Abstract. Volcanoes are an important source of inorganic halogen species into the atmosphere. Chemical processing of these species generates oxidised, highly reactive, halogen species which catalyse considerable O3 destruction within volcanic plumes. A campaign of ground-based in situ O3, SO2 and meteorology measurements was undertaken at the summit of Mount Etna volcano in July–August 2012. At the same time, spectroscopic measurements were made of BrO and SO2 columns in the plume downwind. Depletions of O3 were seen at all in-plume measurement locations, with average O3 depletions ranging from 11–35 nmol mol−1 (15–45%). Atmospheric processing times of the plume were estimated to be between 1 and 4 min. A 1-D numerical model of early plume evolution was also used. It was found that in the early plume O3 was destroyed at an approximately constant rate relative to an inert plume tracer. This is ascribed to reactive halogen chemistry, and the data suggests the majority of the reactive halogen that destroys O3 in the early plume is generated within the crater, including a substantial proportion generated in a high-temperature "effective source region" immediately after emission. The model could approximately reproduce the main measured features of the O3 chemistry. Model results show a strong dependence of the near-vent bromine chemistry on the presence or absence of volcanic NOx emissions and suggest that near-vent O3 measurements can be used as a qualitative indicator of NOx emission.

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Solubility of metals in aerosol samples from Mount Etna during the EPL-REFLECT campaign

10.5194/egusphere-egu2020-9858 ◽

2020 ◽

Author(s):

Chiara Giorio ◽

Sara D'Aronco ◽

Lidia Soldà ◽

Salvatore Giammanco ◽

Alessandro La Spina ◽

...

Keyword(s):

Trace Metals ◽

Human Health ◽

Organic Compounds ◽

Organic Ligand ◽

Mount Etna ◽

Urban Site ◽

Explosive Eruptions ◽

Chemical Components ◽

Volcanic Plume ◽

Volcanic Plumes

Volcanoes emit a chemically complex cocktail of gases and aerosols into the atmosphere, which can affect Earth&#8217;s climate (1) and human health. The vast majority of volcanogenic fatalities involve the obvious thermal and physical injuries resulting from an eruption, but many of the emissions from volcanoes are toxic and include compounds such as sulfates and metals, which are known to disrupt biological systems (2). Yet, there is a lack of knowledge on the toxicity of compounds found in volcanic plumes and their fate in the atmosphere.Research has focussed on the impacts of large-magnitude explosive eruptions. While emissions from many non-explosive eruptions are continuous and prolonged, their climatic and potential effects on human health have not been studied extensively. Once the plume disperses in the atmosphere, the aerosol particle components can mix and interact with oxidants and organic compounds present in the atmosphere. How these chemical components interact and how the interactions affect the Earth&#8217;s climate, particle toxicity and human health is largely unknown especially for trace metals.In the framework of the EPL-REFLECT (Etna Plume Lab &#8211; near-source estimations of Radiative EFfects of voLcanic aErosols for Climate and air quality sTudies), a field campaign on Mount Etna was done in July 2019 in which samples of atmospheric aerosol were collected during non-explosive degassing activity. Samples were collected both at the crater and in a transect following the volcanic plume down slope to the closest inhabited areas. Samples were analysed for trace metals and organic compounds, including solubility tests (3) to assess how tropospheric processing of the aerosol affects metal bioavailability and potentially the toxicity of the aerosol.&#160;(1) von Glasow, R. 2010. Atmospheric chemistry in volcanic plumes. Proceedings of the National Academy of Sciences, vol. 107, pp. 6594&#8211;6599., DOI: 10.1073/pnas.0913164107(2) Weinstein, P., Horwell, C.J., Cook, A. 2013. Volcanic Emissions and Health. In: Essentials of Medical Geology, Springer Netherlands, Dordrecht, pp. 217&#8211;238., DOI: 10.1007/978-94-007-4375-5_10(3) Tapparo, A., Di Marco, V., Badocco, D., D&#8217;Aronco, S., Sold&#224;, L., Pastore, P., Mahon, B.M., Kalberer, M., Giorio, C. 2019. Formation of metal-organic ligand complexes affects solubility of metals in airborne particles at an urban site in the Po Valley. Chemosphere, in press., DOI: 10.1016/j.chemosphere.2019.125025

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Quantification of the depletion of ozone in the plume of Mount Etna

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-2613-2015 ◽

2015 ◽

Vol 15 (5) ◽

pp. 2613-2628 ◽

Cited By ~ 13

Author(s):

L. Surl ◽

D. Donohoue ◽

A. Aiuppa ◽

N. Bobrowski ◽

R. von Glasow

Keyword(s):

Strong Dependence ◽

Source Region ◽

Mount Etna ◽

Volcanic Plumes ◽

Processing Times ◽

Atmospheric Processing ◽

Constant Rate ◽

Halogen Chemistry ◽

Reactive Halogen Species ◽

Halogen Species

Abstract. Volcanoes are an important source of inorganic halogen species into the atmosphere. Chemical processing of these species generates oxidised, highly reactive, halogen species which catalyse considerable O3 destruction within volcanic plumes. A campaign of ground-based in situ O3, SO2 and meteorology measurements was undertaken at the summit of Mount Etna volcano in July/August 2012. At the same time, spectroscopic measurements were made of BrO and SO2 columns in the plume downwind. Depletions of ozone were seen at all in-plume measurement locations, with average O3 depletions ranging from 11–35 nmol mol−1 (15–45%). Atmospheric processing times of the plume were estimated to be between 1 and 4 min. A 1-D numerical model of early plume evolution was also used. It was found that in the early plume O3 was destroyed at an approximately constant rate relative to an inert plume tracer. This is ascribed to reactive halogen chemistry, and the data suggests the majority of the reactive halogen that destroys O3 in the early plume is generated within the crater, including a substantial proportion generated in a high-temperature "effective source region" immediately after emission. The model could approximately reproduce the main measured features of the ozone chemistry. Model results show a strong dependence of the near-vent bromine chemistry on the presence or absence of volcanic NOx emissions and suggest that near-vent ozone measurements can be used as a qualitative indicator of NOx emission.

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Construction of an airborne chemiluminescence ozone monitor for volcanic plumes

10.5194/dach2022-80 ◽

2021 ◽

Author(s):

Ellen Bräutigam ◽

Nicole Bobrowski ◽

Jonas Kuhn ◽

Maja Rüth ◽

Christopher Fuchs ◽

...

Keyword(s):

Trace Gases ◽

Standard Technique ◽

Field Measurements ◽

Ambient Air ◽

Reaction Chamber ◽

Significant Decline ◽

Mount Etna ◽

Volcanic Plume ◽

Volcanic Plumes ◽

Absorption Features

Volcanic plumes contain traces of bromine monoxide, BrO, which catalyze destruction of ozone, O3, mixed into the plume. Therefore, local depletion of O3 in the plume could be possible. However, calculations comparing mixing with the rate of O3 destruction suggest that no significant decline in the O3 concentration should be expected. On the other hand several studies at different volcanoes have found varying degrees of O3 depletion inside the plume. So far, ozone and its concentration distribution in volcanic plumes have only been insufficiently determined. Reliable ozone measurements would make a decisive contribution to the understanding of volcanic plume chemistry. The standard technique for ambient O3 monitoring is the short-path ultraviolet (UV) absorption instrument. But in volcanic plumes this technique suffers from strong interference of the overlapping SO2 absorption features in the UV. SO2 is one of the major compounds in volcanic plumes. We want to overcome this problem by relying on the chemiluminescence (CL) reaction between ozone and ethene, a standard technique for O3 measurement in the 1970s and 1980s, which we found to have no interference from trace gases abundant in volcanic plumes. The key component of a CL O3-instrument is a reaction chamber, where ethene is mixed into the ambient air and a photomultiplier tube detects the resulting photons. Field measurements with existing CL O3-monitors are complicated, because they are usually heavy and bulky. Therefore we designed a more compact and lightweight version (10 kg backpack size CL instrument), which was used in a field study at Mount Etna. However, the campaign was restricted to plumes that are pushed down to ground in areas accessible by foot. Here we report on a further improved version of the instrument weighing around 1 kg, which we can mount onto a drone to carry it into the plume. In particular, we describe the design advances making the reduction in weight and size possible.

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Enhancement of the volcanogenic "bromine explosion" via reactive nitrogen chemistry (Kīlauea volcano, Hawai'i)

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-10313-2010 ◽

2010 ◽

Vol 10 (4) ◽

pp. 10313-10334 ◽

Cited By ~ 1

Author(s):

G. G. Salerno ◽

C. Oppenheimer ◽

V. I. Tsanev ◽

A. J. Sutton ◽

T. J. Roberts ◽

...

Keyword(s):

Active Role ◽

Kilauea Volcano ◽

Molar Ratio ◽

Optical Absorption Spectroscopy ◽

Volcanic Plume ◽

Strongly Correlated ◽

Volcanic Plumes ◽

So2 Flux ◽

Kīlauea Volcano ◽

Halogen Chemistry

Abstract. Since the first detection of bromine monoxide in volcanic plumes attention has focused on the atmospheric synthesis and impact of volcanogenic reactive halogens. We report here new measurements of BrO in the volcanic plume emitted from Kīlauea volcano – the first time reactive halogens have been observed in emissions from a hotspot volcano. Observations were carried out by ground-based Differential Optical Absorption Spectroscopy in 2007 and 2008 at Pu'u'O'o crater, and at the 2008 magmatic vent that opened within Halema'uma'u crater. BrO was readily detected in the Halema'uma'u plume (average column amount of 3×1015 molec cm−2) and its abundance was strongly correlated with that of SO2. However, anticorrelation between NO2 and SO2 (and BrO) abundances in the same plume strongly suggest an active role of NOx in reactive halogen chemistry. The calculated SO2/BrO molar ratio of ~1600 is comparable to observations at other volcanoes, although the BrO mixing ratio is roughly double that observed elsewhere. While BrO was not observed in the Pu'u'O'o plume this was probably merely a result of the detection limit of our measurements and based on understanding of the Summit and East Rift magmatic system we expect reactive halogens to be formed also in the Pu'u'O'o emissions. If this is correct then based on the long term SO2 flux from Pu'u'O'o we calculate that Kīlauea emits ~480 Mg yr−1 of reactive bromine and may thus represent an important source to the tropical Pacific troposphere.

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598 Temperature profiles of sunlight-exposed surfaces in a desert climate: Determining the risks for pavement burns.

Journal of Burn Care & Research ◽

10.1093/jbcr/irab032.248 ◽

2021 ◽

Vol 42 (Supplement_1) ◽

pp. S150-S151

Author(s):

Paul J Chestovich ◽

Richard Z Saroukhanoff ◽

Syed F Saquib ◽

Joseph T Carroll ◽

Carmen E Flores ◽

...

Keyword(s):

Ambient Temperature ◽

Solar Irradiance ◽

Time Of Day ◽

Temperature Measurements ◽

Solar Irradiation ◽

Porous Rock ◽

Solid Materials ◽

Contour Plots ◽

Desert Climate ◽

Sunlight Intensity

Abstract Introduction In the desert climates of the United States, plentiful sunlight and high summer temperatures cause significant burn injuries from hot pavement and other surfaces. Although it is well known that surfaces reach temperatures sufficient to cause full-thickness burns, the peak temperature, time of day, and highest risk materials is not well described. This work measured continuous temperature measurements of six materials in a desert climate over a five-month period. Methods Six different solid materials common in an urban environment were utilized for measurement. Asphalt, brick, concrete, sand, porous rock, and galvanized metal were equipped with thermocouples attached to a data acquisition module. All solid materials except metal were placed in a 2’x2’x3.5” form, and identical samples were placed in both shade and direct sunlight. Ambient temperature was recorded, and sunlight intensity was measured using a pyranometer. Measurement time interval was set at three minutes. A computational fluid dynamics (CFD) model was created using Star CCM+ to validate the data. Contour plots of temperature, solar irradiance, and time of day were created using MiniTab for all surfaces tested. Results 75,000 temperature measurements were obtained from March through August 2020. Maximum recorded temperatures for sunlight-exposed samples of porous rock was 170 F, asphalt 166 F, brick 152 F, concrete 144 F, metal 144 F, and sand 143 F. Peak temperatures were recorded on August 6, 2020 at 2:10 pm, when ambient temperature was 120 F and sunlight intensity 940 W/m2 (Table). Temperatures ranged from 36 F - 56 F higher than identical materials in the shade at the same time. The highest daily temperatures were achieved between 2:00 pm to 4:00 pm due to maximum solar irradiance. Contour plots of surface temperature as function of solar irradiation and time of day were created for all surfaces tested. Nearly identical results obtained from the CFD models to the experimentally collected data, which validated the experimental data. Conclusions Surfaces exposed to direct, continuous sunlight in a desert climate achieve temperatures from 143 F to 170 F in the early afternoon and are high enough to cause significant injury with sufficient exposure. Porous rock reached the highest temperature, followed closely by asphalt. This information is useful to inform the public of the dangers of exposed surfaces in a desert climate.

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A closer look at Arctic ozone loss and polar stratospheric clouds

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-8499-2010 ◽

2010 ◽

Vol 10 (17) ◽

pp. 8499-8510 ◽

Cited By ~ 35

Author(s):

N. R. P. Harris ◽

R. Lehmann ◽

M. Rex ◽

P. von der Gathen

Keyword(s):

Nitric Acid ◽

Climate Models ◽

Empirical Relationship ◽

Early Spring ◽

Aerosol Formation ◽

Polar Stratospheric Clouds ◽

Ozone Loss ◽

Relationship Analysis ◽

Near Ultraviolet ◽

Stratospheric Clouds

Abstract. The empirical relationship found between column-integrated Arctic ozone loss and the potential volume of polar stratospheric clouds inferred from meteorological analyses is recalculated in a self-consistent manner using the ERA Interim reanalyses. The relationship is found to hold at different altitudes as well as in the column. The use of a PSC formation threshold based on temperature dependent cold aerosol formation makes little difference to the original, empirical relationship. Analysis of the photochemistry leading to the ozone loss shows that activation is limited by the photolysis of nitric acid. This step produces nitrogen dioxide which is converted to chlorine nitrate which in turn reacts with hydrogen chloride on any polar stratospheric clouds to form active chlorine. The rate-limiting step is the photolysis of nitric acid: this occurs at the same rate every year and so the interannual variation in the ozone loss is caused by the extent and persistence of the polar stratospheric clouds. In early spring the ozone loss rate increases as the solar insolation increases the photolysis of the chlorine monoxide dimer in the near ultraviolet. However the length of the ozone loss period is determined by the photolysis of nitric acid which also occurs in the near ultraviolet. As a result of these compensating effects, the amount of the ozone loss is principally limited by the extent of original activation rather than its timing. In addition a number of factors, including the vertical changes in pressure and total inorganic chlorine as well as denitrification and renitrification, offset each other. As a result the extent of original activation is the most important factor influencing ozone loss. These results indicate that relatively simple parameterisations of Arctic ozone loss could be developed for use in coupled chemistry climate models.

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Detection of Volcanic Plumes by GPS: the 23 November 2013 Episode on Mt. Etna

Annals of Geophysics ◽

10.4401/ag-6622 ◽

2015 ◽

Vol 57 ◽

Author(s):

Massimo Aranzulla ◽

Flavio Cannavò ◽

Simona Scollo

Keyword(s):

Signal To Noise Ratio ◽

Explosive Eruptions ◽

Volcanic Plume ◽

Test Case ◽

Signal To Noise ◽

Volcanic Plumes ◽

Gps Network ◽

Mt Etna ◽

New Challenges ◽

Aviation Operations

The detection of volcanic plumes produced during explosive eruptions is important to improve our understanding on dispersal processes and reduce risks to aviation operations. The ability of Global Position-ing System (GPS) to retrieve volcanic plumes is one of the new challenges of the last years in volcanic plume detection. In this work, we analyze the Signal to Noise Ratio (SNR) data from 21 permanent stations of the GPS network of the Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, that are located on the Mt. Etna (Italy) flanks. Being one of the most explosive events since 2011, the eruption of November 23, 2013 was chosen as a test-case. Results show some variations in the SNR data that can be correlated with the presence of an ash-laden plume in the atmosphere. Benefits and limitations of the method are highlighted.

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