scholarly journals The mechanism of halogen liberation in the polar troposphere

2004 ◽  
Vol 4 (3) ◽  
pp. 3607-3652 ◽  
Author(s):  
E. Lehrer ◽  
G. Hönninger ◽  
U. Platt
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Gas Phase ◽  
Ozone Depletion ◽  
Primary Source ◽  
Temperature Inversion ◽  
The Arctic ◽  
Ice Surface ◽  
Reactive Halogen Species ◽  
Halogen Species

Abstract. Sudden depletions of tropospheric ozone during spring were reported from the Arctic and also from Antarctic coastal sites. Field studies showed that those depletion events are caused by reactive halogen species, especially bromine compounds. However the source and seasonal variation of reactive halogen species is still not completely understood. There are several indications that the halogen mobilisation from the sea ice surface of the polar oceans may be the most important source for the necessary halogens. Here we present a 1-D model study aimed at determining the primary source of reactive halogens. The model includes gas phase and heterogeneous bromine and chlorine chemistry as well as vertical transport between the surface and the top of the boundary layer. The autocatalytic Br release by photochemical processes (bromine explosion) and subsequent rapid bromine catalysed ozone depletion is well reproduced in the model and the major source of reactive bromine appears to be the sea ice surface. The sea salt aerosol alone is not sufficient to yield the high levels of reactive bromine in the gas phase necessary for fast ozone depletion. However, the aerosol efficiently 'recycles' less reactive bromine species (e.g. HBr) and feeds them back into the ozone destruction cycle. Isolation of the boundary layer air from the free troposphere by a strong temperature inversion was found to be critical for boundary layer ozone depletion to happen. The combination of strong surface inversions and presence of sunlight occurs only during polar spring.

scholarly journals A one dimensional model study of the mechanism of halogen liberation and vertical transport in the polar troposphere

2004 ◽  
Vol 4 (11/12) ◽  
pp. 2427-2440 ◽  
Author(s):  
E. Lehrer ◽  
G. Hönninger ◽  
U. Platt
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Gas Phase ◽  
Ozone Depletion ◽  
Dimensional Model ◽  
One Dimensional ◽  
Ice Surface ◽  
Model Study ◽  
Reactive Halogen Species ◽  
Halogen Species

Abstract. Sudden depletions of tropospheric ozone during spring were reported from the Arctic and also from Antarctic coastal sites. Field studies showed that those depletion events are caused by reactive halogen species, especially bromine compounds. However the source and seasonal variation of reactive halogen species is still not completely understood. There are several indications that the halogen mobilisation from the sea ice surface of the polar oceans may be the most important source for the necessary halogens. Here we present a one dimensional model study aimed at determining the primary source of reactive halogens. The model includes gas phase and heterogeneous bromine and chlorine chemistry as well as vertical transport between the surface and the top of the boundary layer. The autocatalytic Br release by photochemical processes (bromine explosion) and subsequent rapid bromine catalysed ozone depletion is well reproduced in the model and the major source of reactive bromine appears to be the sea ice surface. The sea salt aerosol alone is not sufficient to yield the high levels of reactive bromine in the gas phase necessary for fast ozone depletion. However, the aerosol efficiently "recycles" less reactive bromine species (e.g. HBr) and feeds them back into the ozone destruction cycle. Isolation of the boundary layer air from the free troposphere by a strong temperature inversion was found to be critical for boundary layer ozone depletion to happen. The combination of strong surface inversions and presence of sunlight occurs only during polar spring.

scholarly journals Halogens and their role in polar boundary-layer ozone depletion

2007 ◽  
Vol 7 (16) ◽  
pp. 4375-4418 ◽  
Author(s):  
W. R. Simpson ◽  
R. von Glasow ◽  
K. Riedel ◽  
P. Anderson ◽  
P. Ariya ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Chemistry ◽  
Ozone Depletion ◽  
Complete Removal ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Polar Regions ◽  
Reactive Halogen Species ◽  
Halogen Activation ◽  
Halogen Species

Abstract. During springtime in the polar regions, unique photochemistry converts inert halide salt ions (e.g. Br−) into reactive halogen species (e.g. Br atoms and BrO) that deplete ozone in the boundary layer to near zero levels. Since their discovery in the late 1980s, research on ozone depletion events (ODEs) has made great advances; however many key processes remain poorly understood. In this article we review the history, chemistry, dependence on environmental conditions, and impacts of ODEs. This research has shown the central role of bromine photochemistry, but how salts are transported from the ocean and are oxidized to become reactive halogen species in the air is still not fully understood. Halogens other than bromine (chlorine and iodine) are also activated through incompletely understood mechanisms that are probably coupled to bromine chemistry. The main consequence of halogen activation is chemical destruction of ozone, which removes the primary precursor of atmospheric oxidation, and generation of reactive halogen atoms/oxides that become the primary oxidizing species. The different reactivity of halogens as compared to OH and ozone has broad impacts on atmospheric chemistry, including near complete removal and deposition of mercury, alteration of oxidation fates for organic gases, and export of bromine into the free troposphere. Recent changes in the climate of the Arctic and state of the Arctic sea ice cover are likely to have strong effects on halogen activation and ODEs; however, more research is needed to make meaningful predictions of these changes.

scholarly journals Reproducing springtime Arctic tropospheric ozone depletion events in an outdoor mesocosm sea-ice facility

2021 ◽  
Author(s):  
Zhiyuan Gao ◽  
Nicolas-Xavier Geilfus ◽  
Alfonso Saiz-Lopez ◽  
Feiyue Wang
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Gas Phase ◽  
Ozone Depletion ◽  
Surface Ozone ◽  
Environmental Research ◽  
The Arctic ◽  
Ozone Loss ◽  
Ozone Concentrations ◽  
Air Temperatures

Abstract. The episodic build-up of gas-phase reactive bromine species over sea ice and snowpack in the springtime Arctic plays an important role in the boundary layer, causing annual concurrent depletion of ozone and gaseous elemental mercury during polar sunrise. Extensive studies have shown that these phenomena, known as bromine explosion events (BEEs), ozone depletion events (ODEs) and mercury depletion events (MDEs), respectively, are all triggered by gas-phase reactive bromine species that are photochemically activated from bromide via multi-phase reactions under freezing air temperatures. However, major knowledge gaps exist in both fundamental cryo-photochemical processes causing these events and meteorological conditions that may affect their timing and magnitude. Here, we report an outdoor mesocosm-scale study in which we successfully reproduced ODEs at the Sea-ice Environmental Research Facility (SERF) in Winnipeg, Canada. By monitoring ozone concentrations inside large, acrylic tubes over bromide-enriched artificial seawater during entire sea ice freeze-and-melt cycles, we observed mid-day photochemical ozone loss in winter in the boundary layer air immediately above the sea ice surface in a pattern that is characteristic of BEE-induced ODEs in the Arctic. The importance of UV radiation and the presence of a condensed phase (experimental sea ice or snow) in causing such surface ozone loss was demonstrated by comparing ozone concentrations between UV-transmitting and UV-blocking acrylic tubes under different air temperatures. The ability of reproducing BEE-induced ODEs at a mesocosm scale in a non-polar region provides a new approach to systematically studying the cryo-photochemical and meteorological processes 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 climate change.

scholarly journals Halogens and their role in polar boundary-layer ozone depletion

2007 ◽  
Vol 7 (2) ◽  
pp. 4285-4403 ◽  
Author(s):  
W. R. Simpson ◽  
R. von Glasow ◽  
K. Riedel ◽  
P. Anderson ◽  
P. Ariya ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Chemistry ◽  
Ozone Depletion ◽  
Complete Removal ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Polar Regions ◽  
Reactive Halogen Species ◽  
Halogen Activation ◽  
Halogen Species

Abstract. During springtime in the polar regions, unique photochemistry converts inert halide salts ions (e.g. Br−) into reactive halogen species (e.g. Br atoms and BrO) that deplete ozone in the boundary layer to near zero levels. Since their discovery in the late 1980s, research on ozone depletion events (ODEs) has made great advances; however many key processes remain poorly understood. In this article we review the history, chemistry, dependence on environmental conditions, and impacts of ODEs. This research has shown the central role of bromine photochemistry, but how salts are transported from the ocean and are oxidized to become reactive halogen species in the air is still not fully understood. Halogens other than bromine (chlorine and iodine) are also activated through incompletely understood mechanisms that are probably coupled to bromine chemistry. The main consequence of halogen activation is chemical destruction of ozone, which removes the primary precursor of atmospheric oxidation, and generation of reactive halogen atoms/oxides that become the primary oxidizing species. The different reactivity of halogens as compared to OH and ozone has broad impacts on atmospheric chemistry, including near complete removal and deposition of mercury, alteration of oxidation fates for organic gases, and export of bromine into the free troposphere. Recent changes in the climate of the Arctic and state of the Arctic sea ice cover are likely to have strong effects on halogen activation and ODEs; however, more research is needed to make meaningful predictions of these changes.

scholarly journals Numerical analysis of the chemical kinetic mechanisms of ozone depletion and halogen release in the polar troposphere

2013 ◽  
Vol 13 (9) ◽  
pp. 24171-24222 ◽  
Author(s):  
L. Cao ◽  
H. Sihler ◽  
U. Platt ◽  
E. Gutheil
Keyword(s):  
Boundary Layer ◽  
Surface Area ◽  
Ozone Depletion ◽  
Reaction Rates ◽  
The Arctic ◽  
Strong Impact ◽  
Reactive Surface ◽  
A Value ◽  
Halogen Species

Abstract. In recent years, the role of halogen species (e.g. Br, Cl) in the troposphere of polar regions is investigated after the discovery of their importance for boundary layer ozone destruction in the polar spring. Halogen species take part in an auto-catalytic chemical cycle including key self reactions. In this study, several chemical reaction schemes are investigated, and the importance of specific reactions and their rate constants is identified by a sensitivity analysis. A category of heterogeneous reactions related to HOBr activate halogen ions from sea salt aerosols, fresh sea ice or snow pack, driving the "bromine explosion". In the Arctic, a small amount of NOx may exist, which comes from nitrate contained in the snow, and this NOx may have a strong impact on ozone depletion. The heterogeneous reaction rates are parameterized by considering the aerodynamic resistance, a reactive surface ratio, β, i.e. ratio of reactive surface area to total ground surface area, and the boundary layer height, Lmix. It is found that for β = 1, the ozone depletion process starts after five days and lasts for 40 h for Lmix = 200 m. Ozone depletion duration becomes independent of the height of the boundary layer for about β≥20, and it approaches a value of two days for β=100. The role of nitrogen and chlorine containing species on the ozone depletion rate is studied. The calculation of the time integrated bromine and chlorine atom concentrations suggests a value in the order of 103 for the [Br] / [Cl] ratio, which reveals that atomic chlorine radicals have minor direct influence on the ozone depletion. The NOx concentrations are influenced by different chemical cycles over different time periods. During ozone depletion, the reaction cycle involving the BrONO2 hydrolysis is dominant. A critical value of 0.002 of the uptake coefficient of the BrONO2 hydrolysis reaction at the aerosol and saline surfaces is identified, beyond which the existence of NOx species accelerate the ozone depletion event – for lower values, deceleration occurs.

scholarly journals Analysis of reactive bromine production and ozone depletion in the Arctic boundary layer using 3-D simulations with GEM-AQ: inference from synoptic-scale patterns

2011 ◽  
Vol 11 (8) ◽  
pp. 3949-3979 ◽  
Author(s):  
K. Toyota ◽  
J. C. McConnell ◽  
A. Lupu ◽  
L. Neary ◽  
C. A. McLinden ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Ozone Depletion ◽  
Surface Ozone ◽  
High Arctic ◽  
Heterogeneous Reactions ◽  
The Arctic ◽  
Synoptic Scale ◽  
Arctic Boundary Layer ◽  
Surface Snow

Abstract. Episodes of high bromine levels and surface ozone depletion in the springtime Arctic are simulated by an online air-quality model, GEM-AQ, with gas-phase and heterogeneous reactions of inorganic bromine species and a simple scheme of air-snowpack chemical interactions implemented for this study. Snowpack on sea ice is assumed to be the only source of bromine to the atmosphere and to be capable of converting relatively stable bromine species to photolabile Br2 via air-snowpack interactions. A set of sensitivity model runs are performed for April 2001 at a horizontal resolution of approximately 100 km×100 km in the Arctic, to provide insights into the effects of temperature and the age (first-year, FY, versus multi-year, MY) of sea ice on the release of reactive bromine to the atmosphere. The model simulations capture much of the temporal variations in surface ozone mixing ratios as observed at stations in the high Arctic and the synoptic-scale evolution of areas with enhanced BrO column amount ("BrO clouds") as estimated from satellite observations. The simulated "BrO clouds" are in modestly better agreement with the satellite measurements when the FY sea ice is assumed to be more efficient at releasing reactive bromine to the atmosphere than on the MY sea ice. Surface ozone data from coastal stations used in this study are not sufficient to evaluate unambiguously the difference between the FY sea ice and the MY sea ice as a source of bromine. The results strongly suggest that reactive bromine is released ubiquitously from the snow on the sea ice during the Arctic spring while the timing and location of the bromine release are largely controlled by meteorological factors. It appears that a rapid advection and an enhanced turbulent diffusion associated with strong boundary-layer winds drive transport and dispersion of ozone to the near-surface air over the sea ice, increasing the oxidation rate of bromide (Br−) in the surface snow. Also, if indeed the surface snowpack does supply most of the reactive bromine in the Arctic boundary layer, it appears to be capable of releasing reactive bromine at temperatures as high as −10 °C, particularly on the sea ice in the central and eastern Arctic Ocean. Dynamically-induced BrO column variability in the lowermost stratosphere appears to interfere with the use of satellite BrO column measurements for interpreting BrO variability in the lower troposphere but probably not to the extent of totally obscuring "BrO clouds" that originate from the surface snow/ice source of bromine in the high Arctic. A budget analysis of the simulated air-surface exchange of bromine compounds suggests that a "bromine explosion" occurs in the interstitial air of the snowpack and/or is accelerated by heterogeneous reactions on the surface of wind-blown snow in ambient air, both of which are not represented explicitly in our simple model but could have been approximated by a parameter adjustment for the yield of Br2 from the trigger.

Measurements of bromine monoxide over four halogen activation seasons in the Canadian high Arctic

2020 ◽  
Author(s):  
Kristof Bognar ◽  
Xiaoyi Zhao ◽  
Kimberly Strong ◽  
Rachel Y.-W. Chang ◽  
Udo Frieß ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Vertical Mixing ◽  
Temperature Inversion ◽  
The Arctic ◽  
Optical Absorption Spectroscopy ◽  
Blowing Snow ◽  
Atmospheric Conditions ◽  
Coarse Mode ◽  
Arctic Haze

<p><span>Bromine explosions and corresponding ozone depletion events (ODEs) are common in the Arctic spring. The snowpack on sea ice and sea salt aerosols (SSA) are both thought to release bromine, but the relative contribution of each source is not yet known. Furthermore, the role of atmospheric conditions is not fully understood. Long-term measurements of bromine monoxide (BrO) provide useful insight into the underlying processes of bromine activation. Here we present a four-year dataset (2016-2019) of springtime BrO partial columns retrieved from Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements in Eureka, Canada (80.1° N, 86.4° W). Due to the altitude of the measurement site (610 m), the measurements often represent BrO above the shallow boundary layer, and the strength of the temperature inversion has limited impact on the BrO partial columns. When the boundary layer is deep, however, the effects of the enhanced vertical mixing manifest as an increase in the minimum BrO values (and reduced ODE frequency) for wind speeds of ~8 m/s or greater. We find that BrO events show two modes differentiated by local wind direction and air mass history. Longer time spent in first-year sea ice areas corresponds to increased BrO for one of these modes only. We argue that snow on multi-year ice (salted and acidified by Arctic haze) might also contribute to bromine release. The MAX-DOAS measurements show that high aerosol optical depth is required to maintain lofted BrO. In situ measurements indicate that accumulation mode aerosols (mostly Arctic haze) have no direct correlation with BrO. The presence of coarse mode aerosols, however, is a necessary and sufficient condition for observing enhanced BrO at Eureka. The measurements of coarse mode aerosols are consistent with SSA generated from blowing snow. The good correlation between BrO and coarse mode aerosols (R<sup>2</sup> up to 0.57) supports the view that SSA is a direct source of bromine to the polar troposphere.</span></p>

scholarly journals Polar boundary layer bromine explosion and ozone depletion events in the chemistry-climate model EMAC v2.52: Implementation and evaluation of AirSnow algorithm

2017 ◽  
Author(s):  
Stefanie Falk ◽  
Björn-Martin Sinnhuber
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Atmospheric Chemistry ◽  
Dry Deposition ◽  
Ozone Depletion ◽  
Climate Model ◽  
Surface Ozone ◽  
The Arctic ◽  
Vertical Column ◽  
Model Studies

Abstract. Ozone depletion events (ODE) in the polar boundary layer have been observed frequently during spring-time. Most likely, they are related to events of boundary layer enhancement of bromine. Consequently, increased vertical column densities (VCD) of BrO have been observed from satellites. These so called bromine explosion events have been discussed serving as source of tropospheric BrO at high latitudes. We have implemented a treatment of bromine release and recycling on sea ice and snow covered surfaces in the global chemistry-climate model EMAC (ECHAM/MESSy Atmospheric Chemistry) based on the scheme of Toyota et al. (2011). In this scheme, dry deposition fluxes of HBr, HOBr, and BrNO3 over ice and snow covered surfaces are recycled into Br2 fluxes. In addition, dry deposition of O3, dependent on temperature and sunlight, triggers a Br2 release from surfaces associated with first-year sea ice. Many aspects of observed bromine enhancements and associated episodes of near-complete depletion of boundary layer ozone, both in the Arctic and in the Antarctic, are reproduced by this relatively simple approach. We present first results from our global model studies extending over a full annual cycle, including comparisons with GOME satellite BrO VCD and surface ozone observations.

scholarly journals The NO<sub><i>x</i></sub> dependence of bromine chemistry in the Arctic atmospheric boundary layer

2015 ◽  
Vol 15 (18) ◽  
pp. 10799-10809 ◽  
Author(s):  
K. D. Custard ◽  
C. R. Thompson ◽  
K. A. Pratt ◽  
P B. Shepson ◽  
J. Liao ◽  
...  
Keyword(s):  
Climate Change ◽  
Boundary Layer ◽  
Nitrogen Oxides ◽  
Sea Ice ◽  
Gas Phase ◽  
Atmospheric Chemistry ◽  
The Arctic ◽  
Arctic Boundary Layer ◽  
Large Variability ◽  
The Impact

Abstract. Arctic boundary layer nitrogen oxides (NOx = NO2 + NO) are naturally produced in and released from the sunlit snowpack and range between 10 to 100 pptv in the remote background surface layer air. These nitrogen oxides have significant effects on the partitioning and cycling of reactive radicals such as halogens and HOx (OH + HO2). However, little is known about the impacts of local anthropogenic NOx emission sources on gas-phase halogen chemistry in the Arctic, and this is important because these emissions can induce large variability in ambient NOx and thus local chemistry. In this study, a zero-dimensional photochemical kinetics model was used to investigate the influence of NOx on the unique springtime halogen and HOx chemistry in the Arctic. Trace gas measurements obtained during the 2009 OASIS (Ocean – Atmosphere – Sea Ice – Snowpack) field campaign at Barrow, AK were used to constrain many model inputs. We find that elevated NOx significantly impedes gas-phase halogen radical-based depletion of ozone, through the production of a variety of reservoir species, including HNO3, HO2NO2, peroxyacetyl nitrate (PAN), BrNO2, ClNO2 and reductions in BrO and HOBr. The effective removal of BrO by anthropogenic NOx was directly observed from measurements conducted near Prudhoe Bay, AK during the 2012 Bromine, Ozone, and Mercury Experiment (BROMEX). Thus, while changes in snow-covered sea ice attributable to climate change may alter the availability of molecular halogens for ozone and Hg depletion, predicting the impact of climate change on polar atmospheric chemistry is complex and must take into account the simultaneous impact of changes in the distribution and intensity of anthropogenic combustion sources. This is especially true for the Arctic, where NOx emissions are expected to increase because of increasing oil and gas extraction and shipping activities.

scholarly journals Polar boundary layer bromine explosion and ozone depletion events in the chemistry–climate model EMAC v2.52: implementation and evaluation of AirSnow algorithm

2018 ◽  
Vol 11 (3) ◽  
pp. 1115-1131 ◽  
Author(s):  
Stefanie Falk ◽  
Björn-Martin Sinnhuber
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Atmospheric Chemistry ◽  
Dry Deposition ◽  
Ozone Depletion ◽  
Climate Model ◽  
Surface Ozone ◽  
The Arctic ◽  
In Situ Observation ◽  
Vertical Column

Abstract. Ozone depletion events (ODEs) in the polar boundary layer have been observed frequently during springtime. They are related to events of boundary layer enhancement of bromine. Consequently, increased amounts of boundary layer volume mixing ratio (VMR) and vertical column densities (VCDs) of BrO have been observed by in situ observation, ground-based as well as airborne remote sensing, and from satellites. These so-called bromine explosion (BE) events have been discussed serving as a source of tropospheric BrO at high latitudes, which has been underestimated in global models so far. We have implemented a treatment of bromine release and recycling on sea-ice- and snow-covered surfaces in the global chemistry–climate model EMAC (ECHAM/MESSy Atmospheric Chemistry) based on the scheme of Toyota et al. (2011). In this scheme, dry deposition fluxes of HBr, HOBr, and BrNO3 over ice- and snow-covered surfaces are recycled into Br2 fluxes. In addition, dry deposition of O3, dependent on temperature and sunlight, triggers a Br2 release from surfaces associated with first-year sea ice. Many aspects of observed bromine enhancements and associated episodes of near-complete depletion of boundary layer ozone, both in the Arctic and in the Antarctic, are reproduced by this relatively simple approach. We present first results from our global model studies extending over a full annual cycle, including comparisons with Global Ozone Monitoring Experiment (GOME) satellite BrO VCDs and surface ozone observations.

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