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 Pan-Arctic surface ozone: modelling vs. measurements

2020 ◽  
Vol 20 (24) ◽  
pp. 15937-15967
Author(s):  
Xin Yang ◽  
Anne-M. Blechschmidt ◽  
Kristof Bognar ◽  
Audra McClure-Begley ◽  
Sara Morris ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Surface Ozone ◽  
Open Ocean ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Optical Absorption Spectroscopy ◽  
Sea Spray ◽  
Blowing Snow ◽  
Model Control

Abstract. Within the framework of the International Arctic Systems for Observing the Atmosphere (IASOA), we report a modelling-based study on surface ozone across the Arctic. We use surface ozone from six sites – Summit (Greenland), Pallas (Finland), Barrow (USA), Alert (Canada), Tiksi (Russia), and Villum Research Station (VRS) at Station Nord (North Greenland, Danish realm) – and ozone-sonde data from three Canadian sites: Resolute, Eureka, and Alert. Two global chemistry models – a global chemistry transport model (parallelised-Tropospheric Offline Model of Chemistry and Transport, p-TOMCAT) and a global chemistry climate model (United Kingdom Chemistry and Aerosol, UKCA) – are used for model data comparisons. Remotely sensed data of BrO from the GOME-2 satellite instrument and ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) at Eureka, Canada, are used for model validation. The observed climatology data show that spring surface ozone at coastal sites is heavily depleted, making ozone seasonality at Arctic coastal sites distinctly different from that at inland sites. Model simulations show that surface ozone can be greatly reduced by bromine chemistry. In April, bromine chemistry can cause a net ozone loss (monthly mean) of 10–20 ppbv, with almost half attributable to open-ocean-sourced bromine and the rest to sea-ice-sourced bromine. However, the open-ocean-sourced bromine, via sea spray bromide depletion, cannot by itself produce ozone depletion events (ODEs; defined as ozone volume mixing ratios, VMRs, < 10 ppbv). In contrast, sea-ice-sourced bromine, via sea salt aerosol (SSA) production from blowing snow, can produce ODEs even without bromine from sea spray, highlighting the importance of sea ice surface in polar boundary layer chemistry. Modelled total inorganic bromine (BrY) over the Arctic sea ice is sensitive to model configuration; e.g. under the same bromine loading, BrY in the Arctic spring boundary layer in the p-TOMCAT control run (i.e. with all bromine emissions) can be 2 times that in the UKCA control run. Despite the model differences, both model control runs can successfully reproduce large bromine explosion events (BEEs) and ODEs in polar spring. Model-integrated tropospheric-column BrO generally matches GOME-2 tropospheric columns within ∼ 50 % in UKCA and a factor of 2 in p-TOMCAT. The success of the models in reproducing both ODEs and BEEs in the Arctic indicates that the relevant parameterizations implemented in the models work reasonably well, which supports the proposed mechanism of SSA production and bromide release on sea ice. Given that sea ice is a large source of SSA and halogens, changes in sea ice type and extent in a warming climate will influence Arctic boundary layer chemistry, including the oxidation of atmospheric elemental mercury. Note that this work dose not necessary rule out other possibilities that may act as a source of reactive bromine from the sea ice zone.

Pan-Arctic surface ozone seasonality modified by sea-ice-sourced bromine: modelling vs measurements

2021 ◽  
Author(s):  
Xin Yang ◽  
Anne-M Blechschmidt2 ◽  
Kristof Bognar ◽  
Audra McClure–Begley ◽  
Sara Morris ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Surface Ozone ◽  
Open Ocean ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Sea Spray ◽  
Research Station ◽  
Blowing Snow ◽  
Model Control

&lt;p&gt;Within the framework of the International Arctic Systems for Observing the Atmosphere (IASOA), we report a modelling-based study on surface ozone across the Arctic. We use surface ozone from six sites: Summit (Greenland), Pallas (Finland), Barrow (USA), Alert (Canada), Tiksi (Russia), and Villum Research Station (VRS) at Station Nord (North Greenland, Danish Realm), and ozonesonde data from three Canadian sites: Resolute, Eureka, and Alert. Two global chemistry models: a global chemistry transport model (p-TOMCAT) and a global chemistry climate model (UKCA), are used for model-data comparisons. Remotely sensed data of BrO from the GOME-2 satellite instrument at Eureka, Canada are used for model validation.&lt;/p&gt;&lt;p&gt;The observed climatology data show that spring surface ozone at coastal Arctic is heavily depleted, making ozone seasonality at Arctic coastal sites distinctly different from that at inland sites. Model simulations show that surface ozone can be greatly reduced by bromine chemistry. In April, bromine chemistry can cause a net ozone loss (monthly mean) of 10-20 ppbv, with almost half attributable to open-ocean-sourced bromine and the rest to sea-ice-sourced bromine. However, the open-ocean-sourced bromine, via sea spray bromide depletion, cannot by itself produce ozone depletion events (ODEs) (defined as ozone volume mixing ratios VMRs &lt; 10 ppbv). In contrast, sea-ice-sourced bromine, via sea salt aerosol (SSA) production from blowing snow, can produce ODEs even without bromine from sea spray, highlighting the importance of sea ice surface in polar boundary layer chemistry.&lt;/p&gt;&lt;p&gt;Modelled total inorganic bromine (Br&lt;sub&gt;Y&lt;/sub&gt;) over the Arctic sea ice &amp;#160;is sensitive to model configuration, e.g., under the same bromine loading, Br&lt;sub&gt;Y&lt;/sub&gt; in the Arctic spring boundary layer in the p-TOMCAT control run (i.e., with all bromine emissions) can be 2 times that in the UKCA control run. Despite the model differences, both model control runs can successfully reproduce large bromine explosion events (BEEs) and ODEs in polar spring. Model-integrated tropospheric column BrO generally matches GOME-2 tropospheric columns within ~50% in UKCA and a factor of 2 in p-TOMCAT. The success of the models in reproducing both ODEs and BEEs in the Arctic indicates that the relevant parameterizations implemented in the models work reasonably well, which supports the proposed mechanism of SSA production and bromide release on sea ice. Given that sea ice is a large source of SSA and halogens, changes in sea ice type and extent in a warming climate will influence Arctic boundary layer chemistry, including the oxidation of atmospheric elemental mercury. Note that this work dose not necessary rule out other possibilities that may act as a source of reactive bromine from sea ice zone.&lt;/p&gt;

scholarly journals Enhanced tropospheric BrO over Antarctic sea ice in mid winter observed by MAX-DOAS on board the research vessel Polarstern

2007 ◽  
Vol 7 (12) ◽  
pp. 3129-3142 ◽  
Author(s):  
T. Wagner ◽  
O. Ibrahim ◽  
R. Sinreich ◽  
U. Frieß ◽  
R. von Glasow ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Vertical Mixing ◽  
Satellite Observations ◽  
Research Vessel ◽  
Optical Absorption Spectroscopy ◽  
Back Trajectory ◽  
First Year ◽  
Polar Regions ◽  
Near Surface

Abstract. We present Multi AXis-Differential Optical Absorption Spectroscopy (MAX-DOAS) observations of tropospheric BrO carried out on board the German research vessel Polarstern during the Antarctic winter 2006. Polarstern entered the area of first year sea ice around Antarctica on 24 June 2006 and stayed within this area until 15 August 2006. For the period when the ship cruised inside the first year sea ice belt, enhanced BrO concentrations were almost continuously observed. Outside the first year sea ice belt, typically low BrO concentrations were found. Based on back trajectory calculations we find a positive correlation between the observed BrO differential slant column densities (ΔSCDs) and the duration for which the air masses had been in contact with the sea ice surface prior to the measurement. While we can not completely rule out that in several cases the highest BrO concentrations might be located close to the ground, our observations indicate that the maximum BrO concentrations might typically exist in a (possibly extended) layer around the upper edge of the boundary layer. Besides the effect of a decreasing pH of sea salt aerosol with altitude and therefore an increase of BrO with height, this finding might be also related to vertical mixing of air from the free troposphere with the boundary layer, probably caused by convection over the warm ocean surface at polynyas and cracks in the ice. Strong vertical gradients of BrO and O3 could also explain why we found enhanced BrO levels almost continuously for the observations within the sea ice. Based on our estimated BrO profiles we derive BrO mixing ratios of several ten ppt, which is slightly higher than many existing observations. Our observations indicate that enhanced BrO concentrations around Antarctica exist about one month earlier than observed by satellite instruments. From detailed radiative transfer simulations we find that MAX-DOAS observations are up to about one order of magnitude more sensitive to near-surface BrO than satellite observations. In contrast to satellite observations the MAX-DOAS sensitivity hardly decreases for large solar zenith angles and is almost independent from the ground albedo. Thus this technique is very well suited for observations in polar regions close to the solar terminator. For large periods of our measurements the solar elevation was very low or even below the horizon. For such conditions, most reactive Br-compounds might exist as Br2 molecules and ozone destruction and the removal of reactive bromine compounds might be substantially reduced.

scholarly journals Differentiation of coarse-mode anthropogenic, marine and dust particles in the High Arctic islands of Svalbard

2021 ◽  
Vol 21 (14) ◽  
pp. 11317-11335
Author(s):  
Congbo Song ◽  
Manuel Dall'Osto ◽  
Angelo Lupi ◽  
Mauro Mazzola ◽  
Rita Traversi ◽  
...  
Keyword(s):  
The Arctic ◽  
Dust Particles ◽  
Sea Spray ◽  
Polar Regions ◽  
Blowing Snow ◽  
Long Distance ◽  
Svalbard Archipelago ◽  
Coarse Mode ◽  
Arctic Haze ◽  
Natural Aerosol

Abstract. Understanding aerosol–cloud–climate interactions in the Arctic is key to predicting the climate in this rapidly changing region. Whilst many studies have focused on submicrometer aerosol (diameter less than 1 µm), relatively little is known about the supermicrometer aerosol (diameter above 1 µm). Here, we present a cluster analysis of multiyear (2015–2019) aerodynamic volume size distributions, with diameter ranging from 0.5 to 20 µm, measured continuously at the Gruvebadet Observatory in the Svalbard archipelago. Together with aerosol chemical composition data from several online and offline measurements, we apportioned the occurrence of the coarse-mode aerosols during the study period (mainly from March to October) to anthropogenic (two sources, 27 %) and natural (three sources, 73 %) origins. Specifically, two clusters are related to Arctic haze with high levels of black carbon, sulfate and accumulation mode (0.1–1 µm) aerosol. The first cluster (9 %) is attributed to ammonium sulfate-rich Arctic haze particles, whereas the second one (18 %) is attributed to larger-mode aerosol mixed with sea salt. The three natural aerosol clusters were open-ocean sea spray aerosol (34 %), mineral dust (7 %) and an unidentified source of sea spray-related aerosol (32 %). The results suggest that sea-spray-related aerosol in polar regions may be more complex than previously thought due to short- and long-distance origins and mixtures with Arctic haze, biogenic and likely blowing snow aerosols. Studying supermicrometer natural aerosol in the Arctic is imperative for understanding the impacts of changing natural processes on Arctic aerosol.

scholarly journals The Impact of Warm and Moist Airmass Perturbations on Arctic Mixed-Phase Stratocumulus

2020 ◽  
Vol 33 (22) ◽  
pp. 9615-9628
Author(s):  
Gesa K. Eirund ◽  
Anna Possner ◽  
Ulrike Lohmann
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Lower Troposphere ◽  
Temperature Inversion ◽  
Open Ocean ◽  
Mixed Phase ◽  
Specific Humidity ◽  
The Arctic ◽  
Free Troposphere ◽  
The Impact

AbstractThe Arctic is known to be particularly sensitive to climate change. This Arctic amplification has partially been attributed to poleward atmospheric heat transport in the form of airmass intrusions. Locally, such airmass intrusions can introduce moisture and temperature perturbations. The effect of airmass perturbations on boundary layer and cloud changes and their impact on the surface radiative balance has received increased attention, especially over sea ice with regard to sea ice melt. Utilizing cloud-resolving model simulations, this study addresses the impact of airmass perturbations occurring at different altitudes on stratocumulus clouds for open-ocean conditions. It is shown that warm and moist airmass perturbations substantially affect the boundary layer and cloud properties, even for the relatively moist environmental conditions over the open ocean. The cloud response is driven by temperature inversion adjustments and strongly depends on the perturbation height. Boundary layer perturbations weaken and raise the inversion, which destabilizes the lower troposphere and involves a transition from stratocumulus to cumulus clouds. In contrast, perturbations occurring in the lower free troposphere lead to a lowering but strengthening of the temperature inversion, with no impact on cloud fraction. In simulations where free-tropospheric specific humidity is further increased, multilayer mixed-phase clouds form. Regarding energy balance changes, substantial surface longwave cooling arises out of the stratocumulus break-up simulated for boundary layer perturbations. Meanwhile, the net surface longwave warming increases resulting from thicker clouds for airmass perturbations occurring in the lower free troposphere.

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 Characteristic nature of vertical motions observed in Arctic mixed-phase stratocumulus

2013 ◽  
Vol 13 (11) ◽  
pp. 31079-31125 ◽  
Author(s):  
J. Sedlar ◽  
M. D. Shupe
Keyword(s):  
Vertical Velocity ◽  
Vertical Mixing ◽  
Vertical Motion ◽  
Temperature Inversion ◽  
Arctic Sea Ice ◽  
Cloud Layer ◽  
Mixed Phase ◽  
The Arctic ◽  
Cloud Base ◽  
Mixed Phase Clouds

Abstract. Over the Arctic Ocean, little is known, observationally, on cloud-generated buoyant overturning vertical motions within mixed-phase stratocumulus clouds. Characteristics of such motions are important for understanding the diabatic processes associated with the vertical motions, the lifetime of the cloud layer and its micro- and macrophysical characteristics. In this study, we exploit a suite of surface-based remote sensors over the high Arctic sea ice during a week-long period of persistent stratocumulus in August 2008 to derive the in-cloud vertical motion characteristics. In-cloud vertical velocity skewness and variance profiles are found to be strikingly different from observations within lower-latiatude stratocumulus, suggesting these Arctic mixed-phase clouds interact differently with the atmospheric thermodynamics (cloud tops extending above a stable temperature inversion base) and with a different coupling state between surface and cloud. We find evidence of cloud-generated vertical mixing below cloud base, regardless of surface-cloud coupling state, although a decoupled surface-cloud state occurred most frequently. Detailed case studies are examined focusing on 3 levels within the cloud layer, where wavelet and power spectral analyses are applied to characterize the dominant temporal and horizontal scales associated with cloud-generated vertical motions. In general, we find a positively-correlated vertical motion signal across the full cloud layer depth. The coherency is dependent upon other non-cloud controlled factors, such as larger, mesoscale weather passages and radiative shielding of low-level stratocumulus by multiple cloud layers above. Despite the coherency in vertical velocity across the cloud, the velocity variances were always weaker near cloud top, relative to cloud mid and base. Taken in combination with the skewness, variance and thermodynamic profile characteristics, we observe vertical motions near cloud-top that behave differently than those from lower within the cloud layer. Spectral analysis indicates peak cloud-generated w variance timescales slowed only modestly during decoupled cases relative to coupled; horizontal wavelengths only slightly increased when transitioning from coupling to decoupling. The similarities in scales suggests that perhaps the dominant forcing for all cases is generated from the cloud layer, and it is not the surface forcing that characterizes the time and space scales of in-cloud vertical velocity variance. This points toward the resilient nature of Arctic mixed-phase clouds to persist when characterized by thermodynamic regimes unique to the Arctic.

scholarly journals The role of open lead interactions in atmospheric ozone variability between Arctic coastal and inland sites

Elem Sci Anth ◽  
2016 ◽  
Vol 4 ◽  
Author(s):  
Peter K. Peterson ◽  
Kerri A. Pratt ◽  
William R. Simpson ◽  
Son V. Nghiem ◽  
Lemuel X. Pérez Pérez ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Ozone Depletion ◽  
Surface Ozone ◽  
Optical Absorption Spectroscopy ◽  
Atmospheric Ozone ◽  
Vertical Profiles ◽  
Large Spatial Scale ◽  
Near Surface ◽  
Air Masses

Abstract Boundary layer atmospheric ozone depletion events (ODEs) are commonly observed across polar sea ice regions following polar sunrise. During March-April 2005 in Alaska, the coastal site of Barrow and inland site of Atqasuk experienced ODEs (O3&lt; 10 nmol mol-1) concurrently for 31% of the observations, consistent with large spatial scale ozone depletion. However, 7% of the time ODEs were exclusively observed inland at Atqasuk. This phenomenon also occurred during one of nine flights during the BRomine, Ozone, and Mercury EXperiment (BROMEX), when atmospheric vertical profiles at both sites showed near-surface ozone depletion only at Atqasuk on 28 March 2012. Concurrent in-flight BrO measurements made using nadir scanning differential optical absorption spectroscopy (DOAS) showed the differences in ozone vertical profiles at these two sites could not be attributed to differences in locally occurring halogen chemistry. During both studies, backward air mass trajectories showed that the Barrow air masses observed had interacted with open sea ice leads, causing increased vertical mixing and recovery of ozone at Barrow and not Atqasuk, where the air masses only interacted with tundra and consolidated sea ice. These observations suggest that, while it is typical for coastal and inland sites to have similar ozone conditions, open leads may cause heterogeneity in the chemical composition of the springtime Arctic boundary layer over coastal and inland areas adjacent to sea ice regions.

scholarly journals A parameter model of gas exchange for the seasonal sea ice zone

Ocean Science ◽  
2014 ◽  
Vol 10 (1) ◽  
pp. 17-28 ◽  
Author(s):  
B. Loose ◽  
W. R. McGillis ◽  
D. Perovich ◽  
C. J. Zappa ◽  
P. Schlosser
Keyword(s):  
Boundary Layer ◽  
Gas Exchange ◽  
Sea Ice ◽  
Open Water ◽  
Field Studies ◽  
The Arctic ◽  
Gas Transfer ◽  
Transfer Velocity ◽  
Using Data ◽  
Effective Transfer

Abstract. Carbon budgets for the polar oceans require better constraint on air–sea gas exchange in the sea ice zone (SIZ). Here, we utilize advances in the theory of turbulence, mixing and air–sea flux in the ice–ocean boundary layer (IOBL) to formulate a simple model for gas exchange when the surface ocean is partially covered by sea ice. The gas transfer velocity (k) is related to shear-driven and convection-driven turbulence in the aqueous mass boundary layer, and to the mean-squared wave slope at the air–sea interface. We use the model to estimate k along the drift track of ice-tethered profilers (ITPs) in the Arctic. Individual estimates of daily-averaged k from ITP drifts ranged between 1.1 and 22 m d−1, and the fraction of open water (f) ranged from 0 to 0.83. Converted to area-weighted effective transfer velocities (keff), the minimum value of keff was 10−55 m d−1 near f = 0 with values exceeding keff = 5 m d−1 at f = 0.4. The model indicates that effects from shear and convection in the sea ice zone contribute an additional 40% to the magnitude of keff, beyond what would be predicted from an estimate of keff based solely upon a wind speed parameterization. Although the ultimate scaling relationship for gas exchange in the sea ice zone will require validation in laboratory and field studies, the basic parameter model described here demonstrates that it is feasible to formulate estimates of k based upon properties of the IOBL using data sources that presently exist.

scholarly journals Observations and source investigations of the boundary layer bromine monoxide (BrO) in the Ny-Ålesund Arctic

2018 ◽  
Vol 18 (13) ◽  
pp. 9789-9801 ◽  
Author(s):  
Yuhan Luo ◽  
Fuqi Si ◽  
Haijin Zhou ◽  
Ke Dou ◽  
Yi Liu ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Elemental Mercury ◽  
Arctic Sea Ice ◽  
Optical Absorption Spectroscopy ◽  
Mercury Deposition ◽  
Gaseous Elemental Mercury ◽  
Bay Area ◽  
Short Period ◽  
Kings Bay

Abstract. During polar spring, the presence of reactive bromine in the polar boundary layer is considered to be the main cause of ozone depletion and mercury deposition. However, many uncertainties still remain regarding understanding the mechanisms of the chemical process and source of the bromine. As Arctic sea ice has recently been dramatically reduced, it is critical to investigate the mechanisms using more accurate measurements with higher temporal and spatial resolution. In this study, a typical process of enhanced bromine and depleted ozone in the Ny-Ålesund boundary layer in late April 2015 was observed by applying ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) technique. The results showed that there were bromine monoxide (BrO) slant columns as high as 5.6 × 1014 molec cm−2 above the Kings Bay area on 26 April. Meanwhile, the boundary layer ozone and gaseous elemental mercury (GEM) were synchronously reduced by 85 and 90 %, respectively. Based on the meteorology, sea ice distribution and air mass history, the sea ice in the Kings Bay area, which emerged for only a very short period of time when the enhanced BrO was observed, was considered to be the major source of this bromine enhancement event. The oxidized GEM may be directly deposited onto snow/ice and thereby influence the polar ecosystem.

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