Direct Detection of Atmospheric Atomic Bromine Leading to Mercury and Ozone Depletion

2020 ◽  
Author(s):  
Kerri Pratt ◽  
Siyuan Wang ◽  
Stephen McNamara ◽  
Christopher Moore ◽  
Daniel Obrist ◽  
...  
Keyword(s):  
Ozone Depletion ◽  
Direct Detection ◽  
Bromine Atom ◽  
Critical Role ◽  
Elemental Mercury ◽  
Atmospheric Mercury ◽  
The Arctic ◽  
Molecular Bromine ◽  
Near Surface ◽  
Halogen Chemistry

<p>Bromine atoms play a central role in atmospheric reactive halogen chemistry, depleting ozone and elemental mercury, thereby enhancing deposition of toxic mercury, particularly in the Arctic near-surface troposphere. Yet, direct bromine atom measurements have been missing to date, due to the lack of analytical capability with sufficient sensitivity for ambient measurements. Here we present direct atmospheric bromine atom measurements, conducted in the springtime Arctic near Utqiagvik, Alaska in March 2012. Measured bromine atom levels reached up to 14 ppt (4.2<strong>×</strong>10<sup>8 </sup>atoms cm<sup>-3</sup>) and were up to 3-10 higher than estimates using previous indirect measurements not considering the critical role of molecular bromine. Observed ozone and elemental mercury depletion rates are quantitatively explained by the measured bromine atoms, providing field validation of highly uncertain mercury chemistry. Following complete ozone depletion, elevated bromine concentrations are sustained by photochemical snowpack emissions of molecular bromine and nitrogen oxides, resulting in continued atmospheric mercury depletion. This study shows that measured bromine atoms, resulting from photochemical snowpack production of molecular bromine, can quantitatively explain ozone and mercury loss in the near-surface polar atmosphere.</p>

scholarly journals Direct detection of atmospheric atomic bromine leading to mercury and ozone depletion

2019 ◽  
Vol 116 (29) ◽  
pp. 14479-14484 ◽  
Author(s):  
Siyuan Wang ◽  
Stephen M. McNamara ◽  
Christopher W. Moore ◽  
Daniel Obrist ◽  
Alexandra Steffen ◽  
...  
Keyword(s):  
Ozone Depletion ◽  
Direct Detection ◽  
Bromine Atom ◽  
Critical Role ◽  
Elemental Mercury ◽  
Atmospheric Mercury ◽  
The Arctic ◽  
Molecular Bromine ◽  
Near Surface ◽  
Halogen Chemistry

Bromine atoms play a central role in atmospheric reactive halogen chemistry, depleting ozone and elemental mercury, thereby enhancing deposition of toxic mercury, particularly in the Arctic near-surface troposphere. However, direct bromine atom measurements have been missing to date, due to the lack of analytical capability with sufficient sensitivity for ambient measurements. Here we present direct atmospheric bromine atom measurements, conducted in the springtime Arctic. Measured bromine atom levels reached 14 parts per trillion (ppt, pmol mol−1; 4.2 × 108 atoms per cm−3) and were up to 3–10 times higher than estimates using previous indirect measurements not considering the critical role of molecular bromine. Observed ozone and elemental mercury depletion rates are quantitatively explained by the measured bromine atoms, providing field validation of highly uncertain mercury chemistry. Following complete ozone depletion, elevated bromine concentrations are sustained by photochemical snowpack emissions of molecular bromine and nitrogen oxides, resulting in continued atmospheric mercury depletion. This study provides a breakthrough in quantitatively constraining bromine chemistry in the polar atmosphere, where this chemistry connects the rapidly changing surface to pollutant fate.

Reproducing polar springtime bromine explosion events, ozone depletion events and atmospheric mercury depletion events in an outdoor mesocosm sea-ice facility

2021 ◽  
Author(s):  
Zhiyuan Gao ◽  
Feiyue Wang ◽  
Nicolas-Xavier Geilfus
Keyword(s):  
Sea Ice ◽  
Ozone Depletion ◽  
Polar Region ◽  
Surface Ozone ◽  
Elemental Mercury ◽  
Atmospheric Mercury ◽  
Environmental Research ◽  
The Arctic ◽  
Gaseous Elemental Mercury ◽  
Air Temperatures

<p>Every year during polar sunrise, a series of photochemical events are observed episodically in the troposphere over the Arctic and Antarctic, including bromine explosion events (BEEs), ozone depletion events (ODEs), and mercury depletion events (MDEs). Extensive studies show that all these events are triggered by gas-phase reactive bromine species that are photochemically activated from sea-salt bromide via multi-phase reactions under freezing air temperatures. However, major knowledge gaps exist in both fundamental cryo-photochemical processes and local meteorological conditions that may affect the timing and magnitude of those events. Here, we present an outdoor mesocosm-scale experiment in which we studied the depletion of surface ozone and gaseous elemental mercury at the Sea-ice Environmental Research Facility (SERF) in Winnipeg, Canada, in an urban and non-polar region. Temporal changes in ozone and gaseous elemental mercury concentrations inside acrylic tubes were monitored over bromide-enriched artificial seawater during entire sea ice freeze-and-melt cycles and open water periods. Mid-day photochemical loss of both gas species was observed in the boundary layer air immediately above the sea ice surface, in a pattern that is characteristic of BEE-induced ODEs and MDEs in the Arctic. The importance of UV radiation and sea ice presence in causing such observations was demonstrated by sampling from UV-transmitting and UV-blocking acrylic tubes under different air temperatures. The ability of reproducing mesocosm-scale BEE-induced ODEs and MDEs in a non-polar region provides a new platform with opportunities to systematically study the cryo-photochemical mechanisms leading to BEEs, ODEs, and MDEs in the Arctic, their role in biogeochemical cycles across the ocean-sea ice-atmosphere interfaces, and their sensitivities to a changing climate. </p>

scholarly journals Simulation of atmospheric mercury depletion events (AMDEs) during polar springtime using the MECCA box model

2008 ◽  
Vol 8 (23) ◽  
pp. 7165-7180 ◽  
Author(s):  
Z.-Q. Xie ◽  
R. Sander ◽  
U. Pöschl ◽  
F. Slemr
Keyword(s):  
Aqueous Phase ◽  
Ozone Depletion ◽  
Elemental Mercury ◽  
Atmospheric Mercury ◽  
Box Model ◽  
Rate Coefficients ◽  
Mercury Species ◽  
Phase Reaction ◽  
Gaseous Elemental Mercury ◽  
Sea Salt Aerosol

Abstract. Atmospheric mercury depletion events (AMDEs) during polar springtime are closely correlated with bromine-catalyzed tropospheric ozone depletion events (ODEs). To study gas- and aqueous-phase reaction kinetics and speciation of mercury during AMDEs, we have included mercury chemistry into the box model MECCA (Module Efficiently Calculating the Chemistry of the Atmosphere), which enables dynamic simulation of bromine activation and ODEs. We found that the reaction of Hg with Br atoms dominates the loss of gaseous elemental mercury (GEM). To explain the experimentally observed synchronous depletion of GEM and O3, the reaction rate of Hg+BrO has to be much lower than that of Hg+Br. The synchronicity is best reproduced with rate coefficients at the lower limit of the literature values for both reactions, i.e. kHg+Br≈3×10−13 and kHg+BrO≤1×10−15 cm3 molecule−1 s−1, respectively. Throughout the simulated AMDEs, BrHgOBr was the most abundant reactive mercury species, both in the gas phase and in the aqueous phase. The aqueous-phase concentrations of BrHgOBr, HgBr2, and HgCl2 were several orders of magnitude larger than that of Hg(SO3)22−. Considering chlorine chemistry outside depletion events (i.e. without bromine activation), the concentration of total divalent mercury in sea-salt aerosol particles (mostly HgCl42−) was much higher than in dilute aqueous droplets (mostly Hg(SO3)22−), and did not exhibit a diurnal cycle (no correlation with HO2 radicals).

scholarly journals Active molecular iodine photochemistry in the Arctic

2017 ◽  
Vol 114 (38) ◽  
pp. 10053-10058 ◽  
Author(s):  
Angela R. W. Raso ◽  
Kyle D. Custard ◽  
Nathaniel W. May ◽  
David Tanner ◽  
Matt K. Newburn ◽  
...  
Keyword(s):  
Ozone Depletion ◽  
Radiative Forcing ◽  
Elemental Mercury ◽  
Molecular Iodine ◽  
Atmospheric Composition ◽  
The Arctic ◽  
Ionization Mass ◽  
Gaseous Elemental Mercury ◽  
Cloud Properties ◽  
Iodine Chemistry

During springtime, the Arctic atmospheric boundary layer undergoes frequent rapid depletions in ozone and gaseous elemental mercury due to reactions with halogen atoms, influencing atmospheric composition and pollutant fate. Although bromine chemistry has been shown to initiate ozone depletion events, and it has long been hypothesized that iodine chemistry may contribute, no previous measurements of molecular iodine (I2) have been reported in the Arctic. Iodine chemistry also contributes to atmospheric new particle formation and therefore cloud properties and radiative forcing. Here we present Arctic atmospheric I2and snowpack iodide (I−) measurements, which were conducted near Utqiaġvik, AK, in February 2014. Using chemical ionization mass spectrometry, I2was observed in the atmosphere at mole ratios of 0.3–1.0 ppt, and in the snowpack interstitial air at mole ratios up to 22 ppt under natural sunlit conditions and up to 35 ppt when the snowpack surface was artificially irradiated, suggesting a photochemical production mechanism. Further, snow meltwater I−measurements showed enrichments of up to ∼1,900 times above the seawater ratio of I−/Na+, consistent with iodine activation and recycling. Modeling shows that observed I2levels are able to significantly increase ozone depletion rates, while also producing iodine monoxide (IO) at levels recently observed in the Arctic. These results emphasize the significance of iodine chemistry and the role of snowpack photochemistry in Arctic atmospheric composition, and imply that I2is likely a dominant source of iodine atoms in the Arctic.

scholarly journals Observation of HClO3 and HClO4 in the Arctic atmosphere

2020 ◽  
Author(s):  
Yee Jun Tham ◽  
Nina Sarnela ◽  
Carlos A. Cuevas ◽  
Iyer Siddharth ◽  
Lisa Beck ◽  
...  
Keyword(s):  
Gas Phase ◽  
Ozone Depletion ◽  
Surface Ozone ◽  
Negative Ion ◽  
The Arctic ◽  
Research Station ◽  
Visible Absorption ◽  
Data Set ◽  
Near Surface ◽  
Arctic Atmosphere

<p>Atmospheric halogens chemistry like the catalytic reaction of bromine and chlorine radicals with ozone (O<sub>3</sub>) has been known to cause the springtime surface-ozone destruction in the polar region. Although the initial atmospheric reactions of chlorine with ozone are well understood, the final oxidation steps leading to the formation of chlorate (ClO<sub>3</sub><sup>-</sup>) and perchlorate (ClO<sub>4</sub><sup>-</sup>) remain unclear due to the lack of direct evidence of their presence and fate in the atmosphere. In this study, we present the first high-resolution ambient data set of gas-phase HClO<sub>3</sub> (chloric acid) and HClO<sub>4</sub> (perchlorate acid) obtained from the field measurement at the Villum Research Station, Station Nord, in high arctic North Greenland (81°36’ N, 16°40’ W) during the spring of 2015. A state-of-the-art chemical ionization atmospheric pressure interface time-of-flight mass spectrometer (CI-APi-TOF) was used in negative ion mode with nitrate ion as the reagent ion to detect the gas-phase HClO<sub>3</sub> and HClO<sub>4</sub>. We measured significant level of HClO<sub>3</sub> and HClO<sub>4</sub> only during the springtime ozone depletion events in the Greenland, with concentration up to 9x10<sup>5</sup> molecule cm<sup>-3</sup>. Air mass trajectory analysis shows that the air during the ozone depletion event was confined to near-surface, indicating that the O<sub>3</sub> and surface of sea-ice/snowpack may play important roles in the formation of HClO<sub>3</sub> and HClO<sub>4</sub>. We used high-level quantum-chemical methods to calculate the ultraviolet-visible absorption spectra and cross-section of HClO<sub>3</sub> and HClO<sub>4</sub> in the gas-phase to assess their fates in the atmosphere. Overall, our results reveal the presence of HClO<sub>3</sub> and HClO<sub>4</sub> during ozone depletion events, which could affect the chlorine chemistry in the Arctic atmosphere.</p>

scholarly journals A synthesis of atmospheric mercury depletion event chemistry linking atmosphere, snow and water

2007 ◽  
Vol 7 (4) ◽  
pp. 10837-10931 ◽  
Author(s):  
A. Steffen ◽  
T. Douglas ◽  
M. Amyot ◽  
P. Ariya ◽  
K. Aspmo ◽  
...  
Keyword(s):  
Sea Ice ◽  
Current Knowledge ◽  
Kinetic Studies ◽  
Elemental Mercury ◽  
Atmospheric Mercury ◽  
The Arctic ◽  
Polar Regions ◽  
Environmental Media ◽  
Gaseous Elemental Mercury ◽  
History Of

Abstract. It was discovered in 1995 that, during the spring time, unexpectedly low concentrations of gaseous elemental mercury (GEM) occurred in the Arctic air. This was surprising for a pollutant known to have a long residence time in the atmosphere; however conditions appeared to exist in the Arctic that promoted this depletion of mercury (Hg). This phenomenon is termed atmospheric mercury depletion events (AMDEs) and its discovery has revolutionized our understanding of the cycling of Hg in Polar Regions while stimulating a significant amount of research to understand its impact to this fragile ecosystem. Shortly after the discovery was made in Canada, AMDEs were confirmed to occur throughout the Arctic, sub-Artic and Antarctic coasts. It is now known that, through a series of photochemically initiated reactions involving halogens, GEM is converted to a more reactive species and is subsequently associated to particles in the air and/or deposited to the polar environment. AMDEs are a means by which Hg is transferred from the atmosphere to the environment that was previously unknown. In this article we review the history of Hg in Polar Regions, the methods used to collect Hg in different environmental media, research results of the current understanding of AMDEs from field, laboratory and modeling work, how Hg cycles around the environment after AMDEs, gaps in our current knowledge and the future impacts that AMDEs may have on polar environments. The research presented has shown that while considerable improvements in methodology to measure Hg have been made the main limitation remains knowing the speciation of Hg in the various media. The processes that drive AMDEs and how they occur are discussed. As well, the roles that the snow pack, oceans, fresh water and the sea ice play in the cycling of Hg are presented. It has been found that deposition of Hg from AMDEs occurs at marine coasts and not far inland and that a fraction of the deposited Hg does not remain in the same form in the snow. Kinetic studies undertaken have demonstrated that bromine is the major oxidant depleting Hg in the atmosphere. Modeling results demonstrate that there is a significant deposition of Hg to Polar Regions as a result of AMDEs. Models have also shown that Hg is readily transported to the Arctic from source regions, at times during springtime when this environment is actively transforming Hg from the atmosphere to the snow and ice surfaces. The presence of significant amounts of methyl Hg in snow in the Arctic surrounding AMDEs is important because this species is the link between the environment and impacts to wildlife and humans. Further, much work on methylation and demethylation processes have occurred but are not yet fully understood. Recent changes in the climate and sea ice cover in Polar Regions are likely to have strong effects on the cycling of Hg in this environment; however more research is needed to understand Hg processes in order to formulate meaningful predictions of these changes. Mercury, Atmospheric mercury depletion events (AMDE), Polar, Arctic, Antarctic, Ice

scholarly journals Cyclone-induced surface ozone and HDO depletion in the Arctic

2017 ◽  
Vol 17 (24) ◽  
pp. 14955-14974 ◽  
Author(s):  
Xiaoyi Zhao ◽  
Dan Weaver ◽  
Kristof Bognar ◽  
Gloria Manney ◽  
Luis Millán ◽  
...  
Keyword(s):  
Ozone Depletion ◽  
Deuterium Oxide ◽  
Surface Ozone ◽  
Weddell Sea ◽  
Cloud Layer ◽  
The Arctic ◽  
Blowing Snow ◽  
Near Surface ◽  
Air Masses ◽  
Ice Cloud

Abstract. Ground-based, satellite, and reanalysis datasets were used to identify two similar cyclone-induced surface ozone depletion events at Eureka, Canada (80.1° N, 86.4° W), in March 2007 and April 2011. These two events were coincident with observations of hydrogen deuterium oxide (HDO) depletion, indicating that condensation and sublimation occurred during the transport of the ozone-depleted air masses. Ice clouds (vapour and crystals) and aerosols were detected by lidar and radar when the ozone- and HDO-depleted air masses arrived over Eureka. For the 2007 event, an ice cloud layer was coincident with an aloft ozone depletion layer at 870 m altitude on 2–3 March, indicating this ice cloud layer contained bromine-enriched blowing-snow particles. Over the following 3 days, a shallow surface ozone depletion event (ODE) was observed at Eureka after the precipitation of bromine-enriched particles onto the local snowpack. A chemistry–climate model (UKCA) and a chemical transport model (pTOMCAT) were used to simulate the surface ozone depletion events. Incorporating the latest surface snow salinity data obtained for the Weddell Sea into the models resulted in improved agreement between the modelled and measured BrO concentrations above Eureka. MERRA-2 global reanalysis data and the FLEXPART particle dispersion model were used to study the link between the ozone and HDO depletion. In general, the modelled ozone and BrO showed good agreement with the ground-based observations; however, the modelled BrO and ozone in the near-surface layer are quite sensitive to the snow salinity. HDO depletion observed during these two blowing-snow ODEs was found to be weaker than pure Rayleigh fractionation. This work provides evidence of a blowing-snow sublimation process, which is a key step in producing bromine-enriched sea-salt aerosol.

scholarly journals A synthesis of atmospheric mercury depletion event chemistry in the atmosphere and snow

2008 ◽  
Vol 8 (6) ◽  
pp. 1445-1482 ◽  
Author(s):  
A. Steffen ◽  
T. Douglas ◽  
M. Amyot ◽  
P. Ariya ◽  
K. Aspmo ◽  
...  
Keyword(s):  
Sea Ice ◽  
Current Knowledge ◽  
Kinetic Studies ◽  
Elemental Mercury ◽  
Atmospheric Mercury ◽  
The Arctic ◽  
Polar Regions ◽  
Environmental Media ◽  
Gaseous Elemental Mercury ◽  
Low Concentrations

Abstract. It was discovered in 1995 that, during the spring time, unexpectedly low concentrations of gaseous elemental mercury (GEM) occurred in the Arctic air. This was surprising for a pollutant known to have a long residence time in the atmosphere; however conditions appeared to exist in the Arctic that promoted this depletion of mercury (Hg). This phenomenon is termed atmospheric mercury depletion events (AMDEs) and its discovery has revolutionized our understanding of the cycling of Hg in Polar Regions while stimulating a significant amount of research to understand its impact to this fragile ecosystem. Shortly after the discovery was made in Canada, AMDEs were confirmed to occur throughout the Arctic, sub-Artic and Antarctic coasts. It is now known that, through a series of photochemically initiated reactions involving halogens, GEM is converted to a more reactive species and is subsequently associated to particles in the air and/or deposited to the polar environment. AMDEs are a means by which Hg is transferred from the atmosphere to the environment that was previously unknown. In this article we review Hg research taken place in Polar Regions pertaining to AMDEs, the methods used to collect Hg in different environmental media, research results of the current understanding of AMDEs from field, laboratory and modeling work, how Hg cycles around the environment after AMDEs, gaps in our current knowledge and the future impacts that AMDEs may have on polar environments. The research presented has shown that while considerable improvements in methodology to measure Hg have been made but the main limitation remains knowing the speciation of Hg in the various media. The processes that drive AMDEs and how they occur are discussed. As well, the role that the snow pack and the sea ice play in the cycling of Hg is presented. It has been found that deposition of Hg from AMDEs occurs at marine coasts and not far inland and that a fraction of the deposited Hg does not remain in the same form in the snow. Kinetic studies undertaken have demonstrated that bromine is the major oxidant depleting Hg in the atmosphere. Modeling results demonstrate that there is a significant deposition of Hg to Polar Regions as a result of AMDEs. Models have also shown that Hg is readily transported to the Arctic from source regions, at times during springtime when this environment is actively transforming Hg from the atmosphere to the snow and ice surfaces. The presence of significant amounts of methyl Hg in snow in the Arctic surrounding AMDEs is important because this species is the link between the environment and impacts to wildlife and humans. Further, much work on methylation and demethylation processes has occurred but these processes are not yet fully understood. Recent changes in the climate and sea ice cover in Polar Regions are likely to have strong effects on the cycling of Hg in this environment; however more research is needed to understand Hg processes in order to formulate meaningful predictions of these changes.

scholarly journals Temporal and spatial characteristics of ozone depletion events from measurements in the Arctic

2014 ◽  
Vol 14 (10) ◽  
pp. 4875-4894 ◽  
Author(s):  
J. W. Halfacre ◽  
T. N. Knepp ◽  
P. B. Shepson ◽  
C. R. Thompson ◽  
K. A. Pratt ◽  
...  
Keyword(s):  
Ozone Depletion ◽  
Spatial Scales ◽  
Surface Ozone ◽  
The Arctic ◽  
Environmental Drivers ◽  
Chemical Mechanisms ◽  
Halogen Chemistry ◽  
Temporal And Spatial ◽  
Temporal And Spatial Characteristics ◽  
Ozone Levels

Abstract. Following polar sunrise in the Arctic springtime, tropospheric ozone episodically decreases rapidly to near-zero levels during ozone depletion events (ODEs). Many uncertainties remain in our understanding of ODE characteristics, including the temporal and spatial scales, as well as environmental drivers. Measurements of ozone, bromine monoxide (BrO), and meteorology were obtained during several deployments of autonomous, ice-tethered buoys (O-Buoys) from both coastal sites and over the Arctic Ocean; these data were used to characterize observed ODEs. Detected decreases in surface ozone levels during the onset of ODEs corresponded to a median estimated apparent ozone depletion timescale (based on both chemistry and the advection of O3-depleted air) of 11 h. If assumed to be dominated by chemical mechanisms, these timescales would correspond to larger-than-observed BrO mole fractions based on known chemistry and assumed other radical levels. Using backward air mass trajectories and an assumption that transport mechanisms dominate observations, the spatial scales for ODEs (defined by time periods in which ozone levels ≤15 nmol mol−1) were estimated to be 877 km (median), while areas estimated to represent major ozone depletions (<10 nmol mol−1) had dimensions of 282 km (median). These observations point to a heterogeneous boundary layer with localized regions of active, ozone-destroying halogen chemistry, interspersed among larger regions of previously depleted air that retain reduced ozone levels through hindered atmospheric mixing. Based on the estimated size distribution, Monte Carlo simulations showed it was statistically possible that all ODEs observed could have originated upwind, followed by transport to the measurement site. Local wind speed averages were low during most ODEs (median of ~3.6 m s−1), and there was no apparent dependence on local temperature.

scholarly journals Ten years trends in atmospheric mercury concentrations, meteorological effects and climate variables at Zeppelin, Ny-Ålesund

2013 ◽  
Vol 13 (1) ◽  
pp. 2273-2312
Author(s):  
T. Berg ◽  
K. A. Pfaffhuber ◽  
A. S. Cole ◽  
O. Engelsen ◽  
A. Steffen
Keyword(s):  
Relative Humidity ◽  
Wind Direction ◽  
Elemental Mercury ◽  
Atmospheric Mercury ◽  
The Arctic ◽  
Climate Indices ◽  
Atmospheric Conditions ◽  
Gaseous Elemental Mercury ◽  
Surface Emission ◽  
Wind Speeds

Abstract. Results from ten years of gaseous elemental mercury (GEM) measurements at Zeppelin Station, Ny-Ålesund, Svalbard, show no overall annual trend between 2000 and 2009. Seasonal trend analysis showed significantly decreasing trends in January, February, March and June and significantly increasing trends in May and July through December. Results showed that atmospheric mercury depletion events (AMDEs) were equally distributed between April and May with only a few having been observed in March and June. A negative correlation between AMDEs and temperature is reported and supports earlier observations that AMDEs tend to occur at low temperatures. Lower concentrations of GEM were seen at lower temperatures below a threshold of 0°C. The occurrence of AMDEs and wind direction were well correlated with the lowest GEM measured when the wind direction was from the Arctic Ocean region. Wind speed was found to not correlate with AMDEs, but the lowest GEM concentrations were observed at low wind speeds between 4 and 11 m s−1. AMDEs and relative humidity did not correlate well, but the lowest GEM levels appeared when the relative humidity was between 80 and 90%. Diurnal variation was observed especially during the month March and is likley due to daytime snow surface emission induced by solar radiation. Relationships between GEM concentration and the Northern Hemisphere climate indices were investigated to assess if these climate parameters might reflect different atmospheric conditions that enhance or reduce spring AMDE activity. No consistent pattern was observed.

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