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.

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 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 An aircraft-borne chemical ionization – ion trap mass spectrometer (CI-ITMS) for fast PAN and PPN measurements

2010 ◽  
Vol 3 (5) ◽  
pp. 4313-4354
Author(s):  
A. Roiger ◽  
H. Aufmhoff ◽  
P. Stock ◽  
F. Arnold ◽  
H. Schlager
Keyword(s):  
Boundary Layer ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Ion Trap ◽  
The Arctic ◽  
Arctic Boundary Layer ◽  
Online Calibration ◽  
Mixing Ratios ◽  
Ion Trap Mass Spectrometer ◽  
Research Aircraft

Abstract. An airborne chemical ionization ion trap mass spectrometer instrument (CI-ITMS) has been developed for tropospheric and stratospheric fast in-situ measurements of PAN (peroxyacetyl nitrate) and PPN (peroxypropionyl nitrate). The first scientific deployment of the FASTPEX instrument (FASTPEX = Fast Measurement of Peroxyacyl nitrates) took place in the Arctic during 18 missions aboard the DLR research aircraft Falcon, within the framework of the POLARCAT-GRACE campaign in the summer of 2008. The FASTPEX instrument is described and characteristic properties of the employed ion trap mass spectrometer are discussed. Atmospheric data obtained at altitudes of up to ~12 km are presented, from the boundary layer to the lowermost stratosphere. Data were sampled with a time resolution of 2 s and a 2σ detection limit of 25 pmol mol−1. An isotopically labelled standard was used for a permanent online calibration. For this reason the accuracy of the PAN measurements is better than ±10% for mixing ratios greater than 200 pmol mol−1. PAN mixing ratios in the summer Arctic troposphere were in the order of a few hundred pmol mol−1 and generally correlated well with CO. In the Arctic boundary layer and lowermost stratosphere smaller PAN mixing ratios were observed due to a combination of missing local sources of PAN precursor gases and efficient removal processes (thermolysis/photolysis). PPN, the second most abundant PAN homologue, was measured simultanously. Observed PPN/PAN ratios range between ~0.03 and 0.3.

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 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 A model study of tropospheric impacts of the Arctic ozone depletion 2011

2014 ◽  
Vol 119 (13) ◽  
pp. 7999-8014 ◽  
Author(s):  
Alexey Yu. Karpechko ◽  
Judith Perlwitz ◽  
Elisa Manzini
Keyword(s):  
Ozone Depletion ◽  
The Arctic ◽  
Model Study

scholarly journals Air–snowpack exchange of bromine, ozone and mercury in the springtime Arctic simulated by the 1-D model PHANTAS – Part 2: Mercury and its speciation

2014 ◽  
Vol 14 (8) ◽  
pp. 4135-4167 ◽  
Author(s):  
K. Toyota ◽  
A. P. Dastoor ◽  
A. Ryzhkov
Keyword(s):  
Boundary Layer ◽  
Rate Constants ◽  
Ozone Depletion ◽  
Equilibrium Constants ◽  
Ambient Air ◽  
Reaction Rates ◽  
Chemical Mechanism ◽  
The Arctic ◽  
Trace Constituents ◽  
The Impact

Abstract. Atmospheric mercury depletion events (AMDEs) refer to a recurring depletion of mercury occurring in the springtime Arctic (and Antarctic) boundary layer, in general, concurrently with ozone depletion events (ODEs). To close some of the knowledge gaps in the physical and chemical mechanisms of AMDEs and ODEs, we have developed a one-dimensional model that simulates multiphase chemistry and transport of trace constituents throughout porous snowpack and in the overlying atmospheric boundary layer (ABL). This paper constitutes Part 2 of the study, describing the mercury component of the model and its application to the simulation of AMDEs. Building on model components reported in Part 1 ("In-snow bromine activation and its impact on ozone"), we have developed a chemical mechanism for the redox reactions of mercury in the gas and aqueous phases with temperature dependent reaction rates and equilibrium constants accounted for wherever possible. Thus the model allows us to study the chemical and physical processes taking place during ODEs and AMDEs within a single framework where two-way interactions between the snowpack and the atmosphere are simulated in a detailed, process-oriented manner. Model runs are conducted for meteorological and chemical conditions that represent the springtime Arctic ABL characterized by the presence of "haze" (sulfate aerosols) and the saline snowpack on sea ice. The oxidation of gaseous elemental mercury (GEM) is initiated via reaction with Br-atom to form HgBr, followed by competitions between its thermal decomposition and further reactions to give thermally stable Hg(II) products. To shed light on uncertain kinetics and mechanisms of this multi-step oxidation process, we have tested different combinations of their rate constants based on published laboratory and quantum mechanical studies. For some combinations of the rate constants, the model simulates roughly linear relationships between the gaseous mercury and ozone concentrations as observed during AMDEs/ODEs by including the reaction HgBr + BrO and assuming its rate constant to be the same as for the reaction HgBr + Br, while for other combinations the results are more realistic by neglecting the reaction HgBr + BrO. Speciation of gaseous oxidized mercury (GOM) changes significantly depending on whether or not BrO is assumed to react with HgBr to form Hg(OBr)Br. Similarly to ozone (reported in Part 1), GEM is depleted via bromine radical chemistry more vigorously in the snowpack interstitial air than in the ambient air. However, the impact of such in-snow sink of GEM is found to be often masked by the re-emissions of GEM from the snow following the photo-reduction of Hg(II) deposited from the atmosphere. GOM formed in the ambient air is found to undergo fast "dry deposition" to the snowpack by being trapped on the snow grains in the top ~1 mm layer. We hypothesize that liquid-like layers on the surface of snow grains are connected to create a network throughout the snowpack, thereby facilitating the vertical diffusion of trace constituents trapped on the snow grains at much greater rates than one would expect inside solid ice crystals. Nonetheless, on the timescale of a week simulated in this study, the signal of atmospheric deposition does not extend notably below the top 1 cm of the snowpack. We propose and show that particulate-bound mercury (PBM) is produced mainly as HgBr42− by taking up GOM into bromide-enriched aerosols after ozone is significantly depleted in the air mass. In the Arctic, "haze" aerosols may thus retain PBM in ozone-depleted air masses, allowing the airborne transport of oxidized mercury from the area of its production farther than in the form of GOM. Temperature dependence of thermodynamic constants calculated in this study for Henry's law and aqueous-phase halide complex formation of Hg(II) species is a critical factor for this proposition, calling for experimental verification. The proposed mechanism may explain observed changes in the GOM–PBM partitioning with seasons, air temperature and the concurrent progress of ozone depletion in the high Arctic. The net deposition of mercury to the surface snow is shown to increase with the thickness of the turbulent ABL and to correspond well with the column amount of BrO in the atmosphere.

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.

scholarly journals Bromide and other ions in the snow, firn air, and atmospheric boundary layer at Summit during GSHOX

2010 ◽  
Vol 10 (5) ◽  
pp. 13609-13642 ◽  
Author(s):  
J. E. Dibb ◽  
L. D. Ziemba ◽  
J. Luxford ◽  
P. Beckman
Keyword(s):  
Boundary Layer ◽  
Arctic Basin ◽  
Elemental Mercury ◽  
The Arctic ◽  
Free Troposphere ◽  
Gaseous Elemental Mercury ◽  
Mixing Ratios ◽  
Summer Time ◽  
Trace Concentrations ◽  
Photochemical Activation

Abstract. Measurements of gas phase soluble bromide in the boundary layer and in firn air, and Br− in aerosol and snow, were made at Summit, Greenland (72.5° N, 38.4° W, 3200 m a.s.l.) as part of a larger investigation into the influence of Br chemistry on HOx cycling. The soluble bromide measurements confirm that photochemical activation of Br− in the snow causes release of active Br to the overlying air despite trace concentrations of Br− in the snow (means 15 and 8 nmol Br− kg−1 of snow in 2007 and 2008, respectively). Mixing ratios of soluble bromide above the snow were also found to be very small (mean <1 ppt both years, with maxima of 3 and 4 ppt in 2007 and 2008, respectively), but these levels clearly oxidize and deposit long-lived gaseous elemental mercury and may perturb HOx partitioning. Concentrations of Br− in surface snow tended to increase/decrease in parallel with the specific activities of the aerosol-associated radionuclides 7Be and 210Pb. Earlier work has shown that ventilation of the boundary layer causes simultaneous increases in 7Be and 210Pb at Summit, suggesting there is a pool of Br in the free troposphere above Summit in summer time. Speciation and the source of this free tropospheric Br are not well constrained, but we suggest it may be linked to extensive regions of active Br chemistry in the Arctic basin which are known to cause ozone and mercury depletion events shortly after polar sunrise. If this hypothesis is correct, it implies persistence of the free troposphere Br− for several months after peak Br activation in March/April. Alternatively, there may be a~ubiquitous pool of Br− in the free troposphere, sustained by currently unknown sources and processes.

scholarly journals Iodine oxide in the global marine boundary layer

2014 ◽  
Vol 14 (15) ◽  
pp. 22217-22243 ◽  
Author(s):  
C. Prados-Roman ◽  
C. A. Cuevas ◽  
T. Hay ◽  
R. P. Fernandez ◽  
A. S. Mahajan ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Chemistry ◽  
Ozone Depletion ◽  
Marine Boundary Layer ◽  
Geographical Pattern ◽  
Mixing Ratios ◽  
Field Campaigns ◽  
Ozone Depletion Potential ◽  
Ubiquitous Presence ◽  
Inorganic Precursors

Abstract. Emitted mainly by the oceans, iodine is a halogen compound important for atmospheric chemistry due to its high ozone depletion potential and effect on the oxidizing capacity of the atmosphere. Here we present a comprehensive dataset of iodine oxide (IO) measurements in the open marine boundary layer (MBL) made during the Malaspina 2010 circumnavigation. Results show IO mixing ratios ranging from 0.4 to 1 pmol mol−1 and, complemented with additional field campaigns, this dataset confirms through observations the ubiquitous presence of reactive iodine chemistry in the global marine environment. We use a global model with organic (CH3I, CH2ICl, CH2I2 and CH2IBr) and inorganic (HOI and I2) iodine ocean emissions to investigate the contribution of the different iodine source gases to the budget of IO in the global MBL. In agreement with previous estimates, our results indicate that, globally averaged, the abiotic precursors contribute about 75% to the iodine oxide budget. However, this work reveals a strong geographical pattern in the contribution of organic vs. inorganic precursors to reactive iodine in the global MBL.

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