scholarly journals Br<sub>2</sub>, BrCl, BrO and surface ozone in coastal Antarctica: a meteorological and chemical analysis

2012 ◽  
Vol 12 (4) ◽  
pp. 11035-11077 ◽  
Author(s):  
Z. Buys ◽  
N. Brough ◽  
G. Huey ◽  
D. Tanner ◽  
R. von Glasow ◽  
...  
Keyword(s):  
Ozone Depletion ◽  
Surface Ozone ◽  
Source Region ◽  
The Arctic ◽  
High Temporal Resolution ◽  
Blowing Snow ◽  
Model Calculations ◽  
Air Mass ◽  
Unusual Event ◽  
Mixing Ratios

Abstract. There is much debate over the source of bromine radicals in the atmosphere that drives polar boundary layer ozone depletion events (ODEs), but there is strong evidence to suggest a source associated with the sea ice zone. Here we report the first high temporal resolution measurements of Br2, BrCl and BrO in coastal Antarctica, made using a Chemical Ionisation Mass Spectrometer (CIMS). Mixing ratios ranged from instrumental detection limits to 13 pptv for BrO, 45 pptv for Br2, and 6 pptv for BrCl. We find evidence for blowing snow as a source of reactive bromine both directly during a storm and subsequently from recycling of bromide deposited on the continental snowpack. An unusual event of trans-continental air mass transport might have been responsible for severe surface ozone depletion observed at Halley. The halogen source region was the Bellingshausen Sea, to the west of the Antarctic Peninsula, the air mass having spent 3 1/2 days in complete darkness prior to arrival at Halley. We, further, identify an artefact in daytime BrCl measurements arising from conversion of HOBr, similar to that already identified for CIMS observations of Br2. Model calculations using the MISTRA 0-D model suggest a 50–60% conversion of HOBr to Br2, and 5–10% conversion to BrCl. Careful data filtering enabled us to use the halogen observations, in conjunction with the MISTRA model, to explore the temperature dependence of the Br2:BrCl ratio. We find evidence of a ratio shift towards Br2 at temperatures below ~−21 °C, suggesting a relationship with hydrohalite (NaCl.2H2O) precipitation. This suite of Antarctic data provides the first analogue to similar measurements made in the Arctic.

scholarly journals High temporal resolution Br<sub>2</sub>, BrCl and BrO observations in coastal Antarctica

2013 ◽  
Vol 13 (3) ◽  
pp. 1329-1343 ◽  
Author(s):  
Z. Buys ◽  
N. Brough ◽  
L. G. Huey ◽  
D. J. Tanner ◽  
R. von Glasow ◽  
...  
Keyword(s):  
Temporal Resolution ◽  
Surface Ozone ◽  
Source Region ◽  
Current Theory ◽  
The Arctic ◽  
High Temporal Resolution ◽  
Polar Regions ◽  
Air Mass ◽  
Unusual Event ◽  
Mixing Ratios

Abstract. There are few observations of speciated inorganic bromine in polar regions against which to test current theory. Here we report the first high temporal resolution measurements of Br2, BrCl and BrO in coastal Antarctica, made at Halley during spring 2007 using a Chemical Ionisation Mass Spectrometer (CIMS). We find indications for an artefact in daytime BrCl measurements arising from conversion of HOBr, similar to that already identified for observations of Br2 made using a similar CIMS method. Using the MISTRA model, we estimate that the artefact represents a conversion of HOBr to Br2 of the order of several tens of percent, while that for HOBr to BrCl is less but non-negligible. If the artefact is indeed due to HOBr conversion, then nighttime observations were unaffected. It also appears that all daytime BrO observations were artefact-free. Mixing ratios of BrO, Br2 and BrCl ranged from instrumental detection limits to 13 pptv (daytime), 45 pptv (nighttime), and 6 pptv (nighttime), respectively. We see considerable variability in the Br2 and BrCl observations over the measurement period which is strongly linked to the prevailing meteorology, and thus air mass origin. Higher mixing ratios of these species were generally observed when air had passed over the sea-ice zone prior to arrival at Halley, than from over the continent. Variation in the diurnal structure of BrO is linked to previous model work where differences in the photolysis spectra of Br2 and O3 is suggested to lead to a BrO maximum at sunrise and sunset, rather than a noon-time maxima. This suite of Antarctic data provides the first analogue to similar measurements made in the Arctic, and of note is that our maximum measured BrCl (nighttime) is less than half of the maximum measured during a similar period (spring-time) in the Arctic (also nighttime). This difference in maximum measured BrCl may also be the cause of a difference in the Br2 : BrCl ratio between the Arctic and Antarctic. An unusual event of trans-continental air mass transport appears to have been responsible for severe surface ozone depletion observed at Halley over a 2-day period. The halogen source region appears to be the Bellingshausen Sea, to the west of the Antarctic Peninsula, with the air mass having spent 3 1/2 days in complete darkness crossing the continent prior to arrival at Halley.

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 Signature of Arctic surface ozone depletion events in the isotope anomaly (Δ<sup>17</sup>O) of atmospheric nitrate

2007 ◽  
Vol 7 (5) ◽  
pp. 1451-1469 ◽  
Author(s):  
S. Morin ◽  
J. Savarino ◽  
S. Bekki ◽  
S. Gong ◽  
J. W. Bottenheim
Keyword(s):  
Boundary Layer ◽  
Ozone Depletion ◽  
Surface Ozone ◽  
The Arctic ◽  
Arctic Boundary Layer ◽  
Mixing Ratios ◽  
Atmospheric Nitrate ◽  
Boundary Layer Ozone ◽  
Oxidation Of No ◽  
Arctic Surface

Abstract. We report the first measurements of the oxygen isotope anomaly of atmospheric inorganic nitrate from the Arctic. Nitrate samples and complementary data were collected at Alert, Nunavut, Canada (82°30 ' N, 62°19 ' W) in spring 2004. Covering the polar sunrise period, characterized by the occurrence of severe boundary layer ozone depletion events (ODEs), our data show a significant correlation between the variations of atmospheric ozone (O3) mixing ratios and Δ17O of nitrate (Δ17O(NO−3)). This relationship can be expressed as: Δ17O(NO−3)/‰, =(0.15±0.03)×O3/(nmol mol–1)+(29.7±0.7), with R2=0.70(n=12), for Δ17O(NO−3) ranging between 29 and 35 ‰. We derive mass-balance equations from chemical reactions operating in the Arctic boundary layer, that describe the evolution of Δ17O(NO−3) as a function of the concentrations of reactive species and their isotopic characteristics. Changes in the relative importance of O3, RO2 and BrO in the oxidation of NO during ODEs, and the large isotope anomalies of O3 and BrO, are the driving force for the variability in the measured Δ17O(NO−3) . BrONO2 hydrolysis is found to be a dominant source of nitrate in the Arctic boundary layer, in agreement with recent modeling studies.

scholarly journals Satellite observations of long range transport of a large BrO plume in the Arctic

2010 ◽  
Vol 10 (14) ◽  
pp. 6515-6526 ◽  
Author(s):  
M. Begoin ◽  
A. Richter ◽  
M. Weber ◽  
L. Kaleschke ◽  
X. Tian-Kunze ◽  
...  
Keyword(s):  
Dispersion Model ◽  
High Surface ◽  
Surface Wind ◽  
Life Time ◽  
The Arctic ◽  
Hudson Bay ◽  
Blowing Snow ◽  
Large Area ◽  
Model Calculations ◽  
Air Mass

Abstract. Ozone Depletion Events (ODE) during polar springtime are a well known phenomenon in the Arctic and Antarctic boundary layer. They are caused by the catalytic destruction of ozone by halogens producing reactive halogen oxides like bromine monoxide (BrO). The key halogen bromine can be rapidly transferred into the gas phase in an autocatalytic process – the so called "Bromine Explosion". However, the exact mechanism, which leads to an initial bromine release as well as the influence of transport and chemical processes on BrO, is still not clearly understood. In this study, BrO measurements from the satellite instrument GOME-2 are used together with model calculations with the dispersion model FLEXPART to study an arctic BrO event in March 2007, which could be tracked over several days and a large area. Full BrO activation was observed within one day east of Siberia with subsequent transport to Hudson Bay. The event was linked to a cyclone with very high surface wind speeds, which could have been involved in the production and lifting of aerosols or blowing snow. Considering the short life time of BrO, transported aerosols or snow can also provide the surface for BrO recycling within the plume for several days. The evolution of the BrO plume could be reproduced by FLEXPART simulations of a passive tracer indicating that the activated air mass was transported all the way from Siberia to Hudson Bay. To localise the most probable transport height, model runs initialised in different heights have been performed showing similar transport patterns throughout the troposphere but best agreement with the measurements between the surface and 3 km. The influence of changes in tropopause height on measured BrO values has been considered, but cannot completely explain the observed high BrO values. Backward trajectories from the area of BrO initialisation show upward lifting from the surface up to 3 km and no indication for intrusion of stratospheric air. These observations are consistent with a scenario in which bromine in the air mass was activated on the surface within the cyclone, lifted upwards and transported over several thousand kilometres to Hudson Bay.

scholarly journals Characteristics of tropospheric ozone depletion events in the Arctic spring: analysis of the ARCTAS, ARCPAC, and ARCIONS measurements and satellite BrO observations

2012 ◽  
Vol 12 (7) ◽  
pp. 16219-16257
Author(s):  
J.-H. Koo ◽  
Y. Wang ◽  
T. P. Kurosu ◽  
K. Chance ◽  
A. Rozanov ◽  
...  
Keyword(s):  
Ozone Depletion ◽  
Tropospheric Ozone ◽  
Surface Ozone ◽  
Convective Transport ◽  
The Arctic ◽  
Satellite Measurements ◽  
Air Mass ◽  
Ozone Loss ◽  
Time Lagged

Abstract. Arctic ozone depletion events (ODEs) are due to catalytic ozone loss driven by halogen chemistry. The presence of ODEs is affected not only by in situ chemistry but also by transport including advection of ozone-poor air mass and vertical mixing. To better characterize the ODEs, we analyze the combined set of surface, ozonesonde, and aircraft in situ measurements of ozone and bromine compounds during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) and the Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) experiments (April 2008). Tropospheric BrO columns retrieved from satellite measurements and back trajectories calculations are used to investigate the characteristics of observed ODEs. The implications of the analysis results for the validation of the retrieval of tropospheric column BrO are also discussed. Time-lagged correlation analysis between in situ (surface and ozonesonde) measurements of ozone and satellite derived tropospheric BrO indicates that the ODEs are due to either local halogen-driven ozone loss or short-range (~1 day) transport from nearby regions with ozone depletion. The effect of in situ halogen-driven loss is also evident in the diurnal variation of surface ozone concentrations at Alert, Canada. High-BrO regions revealed by satellite measurements tend to be collocated with first-year sea ice, particularly over the Chukchi Sea. Aircraft observations indicate low-ozone air mass transported from these high-BrO regions. Correlation analyses of ozone with potential temperature and time-lagged tropospheric BrO column show that the vertical extent of local ozone loss is surprisingly deep (1–2 km) at Resolute and Churchill, Canada. The unstable boundary layer during ODEs at Churchill could potentially provide a source of free tropospheric BrO through convective transport and explain the significant negative correlation between free tropospheric ozone and tropospheric BrO column at this site.

scholarly journals Pronounced signature of arctic surface ozone depletion events after polar sunrise on Δ<sup>17</sup>O in atmospheric nitrate

2006 ◽  
Vol 6 (4) ◽  
pp. 6255-6297 ◽  
Author(s):  
S. Morin ◽  
J. Savarino ◽  
S. Bekki ◽  
S. Gong ◽  
J. W. Bottenheim
Keyword(s):  
Boundary Layer ◽  
Ozone Depletion ◽  
Surface Ozone ◽  
Ice Cores ◽  
The Arctic ◽  
Atmospheric Ozone ◽  
Ozone Level ◽  
Arctic Boundary Layer ◽  
Mixing Ratios ◽  
Boundary Layer Ozone

Abstract. We report in this paper the first measurements of the isotopic anomaly of oxygen in Arctic atmospheric inorganic nitrate. Data and samples were collected at Alert, Nunavut, Canada (82°30' N, 62°19' W) in spring 2004. Focusing on the polar sunrise period, characterized by the occurrence of severe boundary layer ozone depletion events (ODEs), our data show a significant correlation between the evolution of atmospheric ozone (O3) mixing ratios and Δ17O in nitrate Δ17O(NO−3)). This relationship can be expressed as: Δ17O(NO−3)/‰=0.15 O3/ (nmol mol−1) + 28.6, with R2=0.70 (n=12), for Δ17O(NO−3) ranging between 29 and 34. To quantitatively interpret this relationship, we derive from mechanisms at play in the arctic boundary layer isotopic mass-balance equations, which depend on the concentrations of reactive species and their isotopic characteristics. Changes in the relative importance of O3, RO2 and BrO in the oxidation of NOx during ODEs, and the large isotopic anomalies that O3 and BrO carry, are the driving force for the high variability in the measured Δ17O(NO−3). BrONO2 hydrolysis is found to be the major source of nitrate in the arctic boundary layer, in agreement with recent modeling studies. In addition, the isotopic fingerprint of the activity of ozone in a relatively stable compound appears somewhat promising in the perspective of using the isotopic composition of nitrate embedded in polar ice-cores as a paleo-indicator of the atmospheric ozone level that may yield an indirect proxy for the oxidative power of past atmospheres.

scholarly journals Cyclone-Induced Surface Ozone and HDO Depletion in the Arctic

2017 ◽  
Author(s):  
Xiaoyi Zhao ◽  
Dan Weaver ◽  
Kristof Bognar ◽  
Gloria Manney ◽  
Luis Millán ◽  
...  
Keyword(s):  
Ozone Depletion ◽  
Transport Model ◽  
Surface Ozone ◽  
Particle Dispersion ◽  
Weddell Sea ◽  
Cloud Layer ◽  
The Arctic ◽  
Blowing Snow ◽  
Near Surface ◽  
Ice Cloud

Abstract. Ground-based, satellite, and reanalysis datasets were used to identify two similar cyclone-induced surface ozone depletion events at Eureka, Canada (80.1º N, 86.4º W), in March 2007 and April 2011. These two events were coincident with observations of HDO depletion, indicating that condensation and sublimation occurred during the transport of the ozone-depleted airmasses. Ice clouds (vapour and crystals) and aerosols were detected by lidar and radar when the ozone- and HDO-depleted airmasses 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 three days, a shallow surface ozone depletion event (ODE) was observed at Eureka after the precipitation of bromine-enriched particles onto the local snow pack. 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 Ozone in the Boundary Layer air over the Arctic Ocean – measurements during the TARA expedition

2009 ◽  
Vol 9 (2) ◽  
pp. 8561-8586
Author(s):  
J. W. Bottenheim ◽  
S. Netcheva ◽  
S. Morin ◽  
S. V. Nghiem
Keyword(s):  
Boundary Layer ◽  
Arctic Ocean ◽  
Ozone Depletion ◽  
Surface Ozone ◽  
The Arctic ◽  
Total Absence ◽  
Trajectory Calculations ◽  
The Arctic Ocean ◽  
Ocean Measurements ◽  
Siberian Coast

Abstract. A full year of measurements of surface ozone over the Arctic Ocean far removed from land is presented (81° N – 88° N latitude). The data were obtained during the drift of the French schooner TARA between September 2006 and January 2008, while frozen in the Arctic Ocean. The data confirm that long periods of virtually total absence of ozone occur in the spring (mid March to mid June) after Polar sunrise. At other times of the year ozone concentrations are comparable to other oceanic observations with winter mole fractions of ca. 30–40 nmol mol−1 and summer minima of ca. 20 nmol mol−1. Contrary to earlier observations from ozone sonde data obtained at Arctic coastal observatories, the ambient temperature was well above −20°C during most ODEs (ozone depletion episodes). Backwards trajectory calculations suggest that during these ODEs the air had previously been in contact with the frozen ocean surface for several days and originated largely from the Siberian coast where several large open flaw leads developed in the spring of 2007.

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

&lt;p&gt;Atmospheric halogens chemistry like the catalytic reaction of bromine and chlorine radicals with ozone (O&lt;sub&gt;3&lt;/sub&gt;) 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 &amp;#64257;nal oxidation steps leading to the formation of chlorate (ClO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;) and perchlorate (ClO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;) 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&lt;sub&gt;3&lt;/sub&gt; (chloric acid) and HClO&lt;sub&gt;4&lt;/sub&gt; (perchlorate acid) obtained from the field measurement at the Villum Research Station, Station Nord, in high arctic North Greenland (81&amp;#176;36&amp;#8217; N, 16&amp;#176;40&amp;#8217; 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&lt;sub&gt;3&lt;/sub&gt; and HClO&lt;sub&gt;4&lt;/sub&gt;. We measured significant level of HClO&lt;sub&gt;3&lt;/sub&gt; and HClO&lt;sub&gt;4&lt;/sub&gt; only during the springtime ozone depletion events in the Greenland, with concentration up to 9x10&lt;sup&gt;5&lt;/sup&gt; molecule cm&lt;sup&gt;-3&lt;/sup&gt;. Air mass trajectory analysis shows that the air during the ozone depletion event was confined to near-surface, indicating that the O&lt;sub&gt;3&lt;/sub&gt; and surface of sea-ice/snowpack may play important roles in the formation of HClO&lt;sub&gt;3&lt;/sub&gt; and HClO&lt;sub&gt;4&lt;/sub&gt;. We used high-level quantum-chemical methods to calculate the ultraviolet-visible absorption spectra and cross-section of HClO&lt;sub&gt;3&lt;/sub&gt; and HClO&lt;sub&gt;4&lt;/sub&gt; in the gas-phase to assess their fates in the atmosphere. Overall, our results reveal the presence of HClO&lt;sub&gt;3&lt;/sub&gt; and HClO&lt;sub&gt;4&lt;/sub&gt; during ozone depletion events, which could affect the chlorine chemistry in the Arctic atmosphere.&lt;/p&gt;

scholarly journals The chemistry influencing ODEs in the Polar Boundary Layer in spring: a model study

2008 ◽  
Vol 8 (2) ◽  
pp. 7391-7453 ◽  
Author(s):  
M. Piot ◽  
R. von Glasow
Keyword(s):  
Boundary Layer ◽  
Ozone Depletion ◽  
Chemical Species ◽  
Field Measurements ◽  
The Arctic ◽  
Direct Reaction ◽  
Mixing Ratios ◽  
Model Study ◽  
Sensitivity Studies ◽  
Chemical Conditions

Abstract. Near-total depletions of ozone have been observed in the Arctic spring since the mid 1980s. The autocatalytic cycles involving reactive halogens are now recognized to be of main importance for Ozone Depletion Events (ODEs) in the Polar Boundary Layer (PBL). We present sensitivity studies using the model MISTRA in the box-model mode on the influence of chemical species on these ozone depletion processes. In order to test the sensitivity of the chemistry under polar conditions, we compared base runs undergoing fluxes of either Br2, BrCl, or Cl2 to induce ozone depletions, with similar runs including a modification of the chemical conditions. The role of HCHO, H2O2, DMS, Cl2, C2H4, C2H6, HONO, NO2, and RONO2 was investigated. Cases with elevated mixing ratios of HCHO, H2O2, DMS, Cl2, and HONO induced a shift in bromine speciation from Br/BrO to HOBr/HBr, while high mixing ratios of C2H6 induced a shift from HOBr/HBr to Br/BrO. Cases with elevated mixing ratios of HONO, NO2, and RONO2 induced a shift to BrNO2/BrONO2. The shifts from Br/BrO to HOBr/HBr accelerated the aerosol debromination, but also increased the total amount of deposited bromine at the surface (mainly via increased deposition of HOBr). These shifts to HOBr/HBr also hindered the BrO self-reaction. In these cases, the ozone depletion was slowed down, where increases in H2O2 and HONO had the greatest effect. The tests with increased mixing ratios of C2H4 highlighted the decrease in HOx which reduced the production of HOBr from bromine radicals. In addition, the direct reaction of C2H4 with bromine atoms led to less available reactive bromine. The aerosol debromination was therefore strongly reduced. Ozone levels were highly affected by the chemistry of C2H4. Cl2-induced ozone depletions were found unrealistic compared to field measurements due to the rapid production of CH3O2, HOx, and ROOH which rapidly convert reactive chlorine to HCl in a "chlorine counter-cycle". This counter-cycle efficiently reduces the concentration of reactive halogens in the boundary layer. Depending on the relative bromine and chlorine mixing ratios, the production of CH3O2, HOx, and ROOH from the counter-cycle can significantly affect the bromine chemistry. Therefore, the presence of both bromine and chlorine in the air may unexpectedly lead to a slow down in ozone destruction. For all NOy species studied (HONO, NO2, RONO2) the chemistry is characterized by an increased bromine deposition on snow reducing the amount of reactive bromine in the air. Ozone is less depleted under conditions of high mixing ratios of NOx. The production of HNO3 led to the acid displacement of HCl, and the release of chlorine out of salt aerosols (Cl2 or BrCl) increased.

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