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Michelle Pantoya - One of the best experts on this subject based on the ideXlab platform.

  • the water Iodine Oxide system a revised mechanism for hydration and dehydration
    RSC Advances, 2017
    Co-Authors: Dylan K. Smith, Michelle Pantoya, Jeffrey S Parkey, Mehmet Kesmez
    Abstract:

    Iodic acids are widely studied in atmospheric and biological applications but their inherent hydrophilic properties introduce complexities that affect their functionality and reactivity. We have shown that iodic acid (HIO3) dehydrates directly into Iodine pentOxide (I2O5) in contradiction to the generally accepted multi-step dehydration mechanism where HIO3 dehydrates into HI3O8 first, then dehydrates into I2O5. The generally accepted mechanism is used to determine the concentration of iodic acid by TGA and is only valid for special conditions. The revised mechanism allows for the determination of concentrations of iodic acids under all conditions, and the more specific conditions where the accepted mechanism is valid are shown. The determination of concentration of iodic acid with the revised dehydration mechanism is dependent on assumptions of residual water and initial concentration of HI3O8. The validity of these assumptions is established by studying the absorption and hydration behavior of I2O5 from atmospheric water. These results will have an impact on the handling and use of Iodine.

  • Effect of environment on Iodine oxidation state and reactivity with aluminum
    Physical chemistry chemical physics : PCCP, 2016
    Co-Authors: Dylan K. Smith, Jena Mccollum, Michelle Pantoya
    Abstract:

    Iodine Oxide is a highly reactive solid oxidizer and with its abundant generation of Iodine gas during reaction, this oxidizer also shows great potential as a biocidal agent. A problem with using I2O5 in an energetic mixture is its highly variable reactive behavior. This study isolates the variable reactivity associated with I2O5 as a function of its chemical reaction in various environments. Specifically, aluminum fuel and Iodine Oxide powder are combined using a carrier fluid to aid intermixing. The carrier fluid is shown to significantly affect the oxidation state of Iodine Oxide, thereby affecting the reactivity of the mixture. Four carrier fluids were investigated ranging in polarity and water miscibility in increasing order from hexane < acetone < isopropanol < water as well as untreated, dry-mixed reactants. Oxidation state and reactivity were examined with experimental techniques including X-ray photoelectric spectroscopy (XPS) and differential scanning calorimetry (DSC). Results are compared with thermal equilibrium simulations. Flame speeds increased with polarity of the fluid used to intermix the powder and ranged from 180 to 1202 m s(-1). The I2O5 processed in the polar fluids formed hydrated states of Iodine Oxide: HIO3 and HI3O8; and, the nonpolar and dry-mixed samples formed: I2O4 and I4O9. During combustion, the hydrated Iodine Oxides rapidly dehydrated from HIO3 to HI3O8 and from HI3O8 to I2O5. Both steps release 25% of their mass as vapor during combustion. Increased gas generation enhances convective energy transport and accounts for the increase in reactivity seen in the mixtures processed in polar fluids. These results explain the chemical mechanisms underlying the variable reactivity of I2O5 that are a function of the Oxide's highly reactive nature with its surrounding environment. These results will significantly impact the selection of carrier fluid in the synthesis approach for Iodine containing reactive mixtures.

  • Exothermic surface reactions in alumina–aluminum shell–core nanoparticles with Iodine Oxide decomposition fragments
    Journal of Nanoparticle Research, 2014
    Co-Authors: Oliver Mulamba, Michelle Pantoya
    Abstract:

    A pre-ignition reaction (PIR) once thought to be unique to aluminum (Al) and fluorine-based oxidizer reactions is observed for aluminum and an Iodine-containing oxidizer. This PIR is exothermic and precedes the main exothermic reaction corresponding to aluminum combustion. For the aluminum and Iodine Oxide system, exothermic surface chemistry was recently predicted for I–O fragments forming bridge bonds with the alumina passivation shell using first principle calculations, but now has been observed experimentally. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) were used to assess aluminum and Iodine pentOxide (I_2O_5) powder mixtures. Various equivalence ratios were examined and found to affect the PIR onset temperature. Prior to this work, the PIR was attributed solely to surface reactions of the halogen with the Al_2O_3 surface, but, results shown here indicate that both the alumina surface and aluminum core contribute to a PIR and a minimum activation energy is necessary for PIR production.

  • exothermic surface reactions in alumina aluminum shell core nanoparticles with Iodine Oxide decomposition fragments
    Journal of Nanoparticle Research, 2014
    Co-Authors: Oliver Mulamba, Michelle Pantoya
    Abstract:

    A pre-ignition reaction (PIR) once thought to be unique to aluminum (Al) and fluorine-based oxidizer reactions is observed for aluminum and an Iodine-containing oxidizer. This PIR is exothermic and precedes the main exothermic reaction corresponding to aluminum combustion. For the aluminum and Iodine Oxide system, exothermic surface chemistry was recently predicted for I–O fragments forming bridge bonds with the alumina passivation shell using first principle calculations, but now has been observed experimentally. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) were used to assess aluminum and Iodine pentOxide (I2O5) powder mixtures. Various equivalence ratios were examined and found to affect the PIR onset temperature. Prior to this work, the PIR was attributed solely to surface reactions of the halogen with the Al2O3 surface, but, results shown here indicate that both the alumina surface and aluminum core contribute to a PIR and a minimum activation energy is necessary for PIR production.

John M. C. Plane - One of the best experts on this subject based on the ideXlab platform.

  • The first steps of Iodine gas-to-particle conversion as seen in the lab: constraints on the role of Iodine Oxides and oxyacids
    2020
    Co-Authors: Juan Carlos Gómez Martín, John M. C. Plane, Manoj Kumar, Joseph S Francisco, Thomas R. Lewis, Alfonso Saiz-lopez
    Abstract:

    &lt;p&gt;The photooxidation of gas phase Iodine-bearing molecules emitted by marine biota leads to intense particle nucleation events in the coastal and polar marine boundary layer&lt;sup&gt;1-3&lt;/sup&gt;. The ubiquity of Iodine in the marine atmospheric environment&lt;sup&gt;4-7&lt;/sup&gt; has suggested that this may be a previously unrecognized global source of new aerosol particles&lt;sup&gt;8&lt;/sup&gt;. Atmospheric modeling is required in order to evaluate the importance of this process, but a substantial lack of understanding of the gas-to-particle conversion mechanism is hindering this effort, especially regarding the gas phase chemistry of the nucleating molecules (Iodine Oxides&lt;sup&gt;9&lt;/sup&gt;&lt;sup&gt;,&lt;/sup&gt;&lt;sup&gt;10&lt;/sup&gt; and/or oxyacids&lt;sup&gt;7&lt;/sup&gt;) and the formation kinetics of molecular clusters. To address this problem, we have conducted new flow tube laboratory experiments where pulsed laser photolysis or continuous broad-band photolysis of I&lt;sub&gt;2&lt;/sub&gt;/O&lt;sub&gt;3&lt;/sub&gt; mixtures&amp;#160; in air are used to generate Iodine radicals in the presence of atmospherically representative mixing ratios of water vapor. The molecular reactants and the resulting molecular products are detected by time-resolved VUV laser photo-ionization time-of-flight mass spectrometry. High-level quantum chemistry and master equation calculations and gas kinetics modelling are used to analyse the experimental data. In this presentation we discuss our results and their implications for the interpretation of field meassurements and for the implementatiion of an Iodine Oxide particle formation mechanism in atmospheric models.&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;1. Hoffmann, T., O'Dowd, C. D. &amp; Seinfeld, J. H. Iodine Oxide homogeneous nucleation: An explanation for coastal new particle production. Geophys. Res. Lett. &lt;strong&gt;28&lt;/strong&gt;, 1949-1952 (2001).&lt;/p&gt;&lt;p&gt;2. McFiggans, G. et al. Direct evidence for coastal Iodine particles from Laminaria macroalgae - linkage to emissions of molecular Iodine. Atmos. Chem. Phys. &lt;strong&gt;4&lt;/strong&gt;, 701-713 (2004).&lt;/p&gt;&lt;p&gt;3. O'Dowd, C. D. et al. Marine aerosol formation from biogenic Iodine emissions. Nature &lt;strong&gt;417&lt;/strong&gt;, 632-636 (2002).&lt;/p&gt;&lt;p&gt;4. Prados-Roman, C. et al. Iodine Oxide in the global marine boundary layer. Atmos. Chem. Phys. &lt;strong&gt;15&lt;/strong&gt;, 583-593, doi:10.5194/acp-15-583-2015 (2015).&lt;/p&gt;&lt;p&gt;5. Sch&amp;#246;nhardt, A. et al. Simultaneous satellite observations of IO and BrO over Antarctica. Atmos. Chem. Phys. &lt;strong&gt;12&lt;/strong&gt;, 6565-6580, doi:10.5194/acp-12-6565-2012 (2012).&lt;/p&gt;&lt;p&gt;6. Mahajan, A. S. et al. Concurrent observations of atomic Iodine, molecular Iodine and ultrafine particles in a coastal environment. Atmos. Chem. Phys. &lt;strong&gt;10&lt;/strong&gt;, 27227-27253 (2010).&lt;/p&gt;&lt;p&gt;7. Sipil&amp;#228;, M. et al. Molecular-scale evidence of aerosol particle formation via sequential addition of HIO3. Nature &lt;strong&gt;537&lt;/strong&gt;, 532-534, doi:10.1038/nature19314 (2016).&lt;/p&gt;&lt;p&gt;8. Saiz-Lopez, A. et al. Atmospheric Chemistry of Iodine. Chem. Rev. &lt;strong&gt;112&lt;/strong&gt;, 1773&amp;#8211;1804, doi:DOI: 10.1021/cr200029u (2012).&lt;/p&gt;&lt;p&gt;9. G&amp;#243;mez Mart&amp;#237;n, J. C. et al. On the mechanism of Iodine Oxide particle formation. Phys. Chem. Chem. Phys. &lt;strong&gt;15&lt;/strong&gt;, 15612-15622, doi:10.1039/c3cp51217g (2013).&lt;/p&gt;&lt;p&gt;10. Saunders, R. W., Mahajan, A. S., G&amp;#243;mez Mart&amp;#237;n, J. C., Kumar, R. &amp; Plane, J. M. C. Studies of the Formation and Growth of Aerosol from Molecular Iodine Precursor. Z. Phys. Chem. &lt;strong&gt;224&lt;/strong&gt;, 1095-1117 (2010).&lt;/p&gt;

  • On the mechanism of Iodine Oxide particle formation
    Physical chemistry chemical physics : PCCP, 2013
    Co-Authors: J. C. Gómez Martín, John M. C. Plane, Óscar Gálvez, M. T. Baeza-romero, Trevor Ingham, Mark A. Blitz
    Abstract:

    The formation of atmospherically relevant Iodine Oxides IxOy (x = 1,…,3, y = 1,…,7) has been studied experimentally using time-of-flight mass spectrometry combined with a soft ionisation source, complemented with ab initio electronic structure calculations of ionisation potentials and bond energies at a high level of theory presented in detail in the accompanying paper (Galvez et al., 2013). For the first time, direct experimental evidence of the I2Oy (y = 1,…,5) molecules in the gas phase has been obtained. These chemical species are observed alongside their precursors (IO and OIO) in experiments where large amounts of aerosol are also generated. The measured relative concentrations of the IxOy molecules and their dependence on ozone concentration have been investigated by using chemical modelling and rate theory calculations. It is concluded that I2O4 is the most plausible candidate to initiate nucleation, while the contribution of I2O5 in the initial steps is likely to be marginal. The absence of large I3Oy (y = 3,…,6) peaks in the mass spectra and the high stability of the I2O4–I2O4 dimer indicate that dimerisation of I2O4 is the key step in Iodine Oxide particle nucleation.

  • Atmospheric Iodine levels influenced by sea surface emissions of inorganic Iodine
    Nature Geoscience, 2013
    Co-Authors: Lucy J Carpenter, Samantha M. Macdonald, Marvin D. Shaw, Ravi Kumar, Russell W. Saunders, Rajendran Parthipan, Julie Wilson, John M. C. Plane
    Abstract:

    Naturally occurring bromine- and Iodine-containing compounds substantially reduce regional, and possibly global, tropospheric ozone levels. Experimental and model results suggest that the reaction of ozone with iodide could account for around 75% of observed Iodine Oxide levels over the tropical Atlantic Ocean. Naturally occurring bromine- and Iodine-containing compounds substantially reduce regional, and possibly even global, tropospheric ozone levels^ 1 , 2 , 3 , 4 . As such, these halogen gases reduce the global warming effects of ozone in the troposphere^ 5 , and its capacity to initiate the chemical removal of hydrocarbons such as methane. The majority of halogen-related surface ozone destruction is attributable to Iodine chemistry^ 2 . So far, organic Iodine compounds have been assumed to serve as the main source of oceanic Iodine emissions^ 1 , 6 , 7 , 8 , 9 . However, known organic sources of atmospheric Iodine cannot account for gas-phase Iodine Oxide concentrations in the lower troposphere over the tropical oceans^ 3 , 4 . Here, we quantify gaseous emissions of inorganic Iodine following the reaction of iodide with ozone in a series of laboratory experiments. We show that the reaction of iodide with ozone leads to the formation of both molecular Iodine and hypoiodous acid. Using a kinetic box model of the sea surface layer and a one-dimensional model of the marine boundary layer, we show that the reaction of ozone with iodide on the sea surface could account for around 75% of observed Iodine Oxide levels over the tropical Atlantic Ocean. According to the sea surface model, hypoiodous acid—not previously considered as an oceanic source of Iodine—is emitted at a rate ten-fold higher than that of molecular Iodine under ambient conditions.

  • Glass formation and unusual hygroscopic growth of iodic acid solution droplets with relevance for Iodine Oxide particles in the coastal marine boundary layer
    2012
    Co-Authors: Benjamin J. Murray, Rw Saunders, Allen E. Haddrell, S. Peppe, J. F. Davies, Jonathan P. Reid, Debbie O'sullivan, H. C. Price, R. Kumar, John M. C. Plane
    Abstract:

    Abstract. Iodine Oxide particles are known to nucleate in the marine boundary layer where gas phase molecular Iodine and organoIodine species are produced by macroalgae. There has been some debate over the chemical identity of these particles. Hygroscopic measurements have been used to infer that they are composed of insoluble I2O4, while elemental analysis of laboratory generated particles suggests soluble I2O5 or its hydrated form iodic acid, HIO3 (I2O5 · H2O). In this paper we explore the response of super-micron sized aqueous iodic acid solution droplets to varying humidity using both Raman microscopy and single particle electrodynamic traps. These measurements reveal that the propensity of an iodic acid solution droplet to crystallise is negligible on drying to ~0% relative humidity (RH). On applying mechanical pressure to these droplets they shatter in a manner consistent with an ultra-viscous liquid or a brittle glass, but subsequent water uptake between 10 and 20% RH causes their viscosity to reduce sufficiently that the cracked droplets flow and merge. The persistence of iodic acid solution in an amorphous state, rather than a crystalline state, suggests they will more readily accommodate other condensable material and are therefore more likely to grow to sizes where they may serve as cloud condensation nuclei. On increasing the humidity to ~90% the mass of the droplets only increases by ~20% with a corresponding increase in radius of only ~6 %, which is remarkably small for a highly soluble material. We suggest that the small growth factor of aqueous iodic acid solution droplets is consistent with the small aerosol growth factors observed in field experiments.

  • quantum chemical calculations on a selection of Iodine containing species io oio ino3 io 2 i2o3 i2o4 and i2o5 of importance in the atmosphere
    Physical Chemistry Chemical Physics, 2008
    Co-Authors: Nikolas Kaltsoyannis, John M. C. Plane
    Abstract:

    The electronic and geometric structures of the title complexes are studied quantum chemically using ab initio and density functional approaches. Coupled cluster calculations at the scalar relativistic (basis set) level are performed, and the results are corrected for spin–orbit coupling using data from relativistic density functional theory studies. The heats of formation (kJ mol−1) at 298 K are found to be: IO3 147.8, INO3 33.1, OIO 110.1, I2O3 64.0, I2O4 111.3, I2O5 33.0, IOIO 141.3, IOOI 179.9 and OI(I)O 157.9. These data are used to draw a number of conclusions regarding three important aspects of Iodine chemistry in the marine boundary layer. (i) Although the IO self reaction produces the asymmetric dimer, IOIO, it is unlikely that this species plays a further role in the atmosphere as it is short-lived. (ii) INO3 is sufficiently stable to explain the kinetics of the recombination reaction between IO and NO2, and the reaction between I2 and NO3 to produce I + INO3 is almost certainly the major source of Iodine Oxides at night. (iii) The higher Iodine Oxides I2O3 and I2O5 are very stable molecules, by contrast to the OIO dimer, I2O4, which is much less stable but which should still survive long enough in the marine boundary layer to provide a building block for Iodine Oxide particle formation.

Ulrich Platt - One of the best experts on this subject based on the ideXlab platform.

  • Observations of high concentrations of I2 and IO in coastal air supporting Iodine‐Oxide driven coastal new particle formation
    Geophysical Research Letters, 2010
    Co-Authors: Ru-jin Huang, Ulrich Platt, K. Seitz, T. Neary, Colin D. O'dowd, Thorsten Hoffmann
    Abstract:

    [1] Theoretical studies have predicted that concentrations of gaseous I2 and IO of the order of 80–100 ppt and 40–50 ppt, respectively, are required in coastal air to account for photochemically-driven coastal new-particle formation events to occur. However, measurements reported to date (i.e., ∼20 ppt I2, ≤ 10 ppt IO) have not supported the required model predictions. Here, we present measurements of high concentrations of I2 and IO in N.E. Atlantic marine air on the west coast of Ireland. The maximum mixing ratios of daytime I2 and IO over the seaweed beds during low tide were 302 ppt and 35 ppt, respectively. The I2 distribution was rather inhomogeneous, even at the inter-tidal zone, but closely related to the macroalgae biomass abundance. New particle formation bursts were frequently observed during daytime hours with the concentrations up to 4.5 × 105 particles cm−3 during low-tide conditions, and the concentrations of ultra-fine particles were positively correlated with the IO concentrations. Considering the constraints set out in theoretical studies for new particle formation via condensation of condensable Iodine Oxide vapours, the results reported here clearly demonstrate that the molecular Iodine and Iodine monOxide concentrations in coastal air are sufficient to meet the theoretical precursor concentrations required to drive intensive coastal new-particle formation from higher order condensable Iodine Oxides.

  • Iodine Oxide in the Dead Sea Valley: Evidence for inorganic sources of boundary layer IO
    Journal of Geophysical Research, 2005
    Co-Authors: Jutta Zingler, Ulrich Platt
    Abstract:

    [1] The importance of Iodine Oxide (IO) in tropospheric boundary layer chemistry has been well established in the last decade. Iodine-containing radicals have been detected in regions of high biological productivity. To date, most explanations assume biogenic precursors (e.g., emission of iodocarbons). In a 2 week field campaign at the Dead Sea, Israel, IO was found to exceed the detection limit (0.3–2 parts per trillion (ppt)) almost daily, with peak levels topping 10 ppt. Macro algae are nonexistent because of the water's high salinity. The Dead Sea's microbiology is discussed in detail, and organic sources of Iodine Oxide are found to be of minor importance. Thus the site can be treated as a unique place for the investigation of inorganic sources of IO. Such processes have recently been included in model studies. Our study focuses on the first direct evidence for inorganic sources of reactive boundary layer Iodine. Heterogeneous Iodine release induced by photolysis, liquid phase ozone reactions, or catalytic HOX interactions are discussed as well as NOx chemistry.

  • Spectroscopic measurements of tropospheric Iodine Oxide at Neumayer Station, Antarctica
    Geophysical Research Letters, 2001
    Co-Authors: Udo Frieß, Thomas Wagner, I. Pundt, Klaus Pfeilsticker, Ulrich Platt
    Abstract:

    First measurements of Iodine Oxide (IO) in the Antarctic troposphere are reported. Since March 1999, a newly developed dual channel spectrograph has been continuously performing Differential Opti- cal Absorption Spectroscopy (DOAS) measurements of zenith scattered sunlight at Neumayer-Station, Antarc- tica (70o39  S, 8o15  W). The spectral signature of IO was clearly detected by observing five vibrational ab- sorption bands located in the wavelength region be- tween 415 and 461 nm. The observed diurnal variation of IO is characterized by a rapid decrease in the dif- ferential slant column density (DSCD) with increasing solar zenith angle (SZA) during twilight. This observa- tion points to a fast conversion of reactive Iodine into its nighttime reservoir species. It also strongly indicates that the detected IO is located in the troposphere. The decrease of the IO DSCD of up to 1.10 TM molec/cm 2 between 80 o and 95 o SZA is unexpectedly large. Un- der the assumption that IO is located in the marine boundary layer (MBL) (below 2 kin), IO mixing ratios may reach up to 10 ppt. The seasonal variation shows higher IO amounts during summer than during winter. This finding is possibly caused by the smaller distance to the open sea, where the iodocarbons are emitted, and by the more efficient photodissociation of the or- ganic Iodine precursors.

  • Chemistry of Halogen Oxides in the Troposphere: Comparison of Model Calculations with Recent Field Data
    Journal of Atmospheric Chemistry, 1999
    Co-Authors: Jochen Stutz, Björn Alicke, Kai Hebestreit, Ulrich Platt
    Abstract:

    Reactive halogen species (RHS = X, XO, HOX, OXO; X = Cl, Br, I) are known to have an important influence on the chemistry in the polar boundary layer (BL), where they are responsible for ozone depletion events in spring. Recent field campaigns at Mace Head, Ireland, and the Dead Sea, Israel, identified for the first time Iodine Oxide (IO) at mixing ratios of up to 6.6 ppt and 90 ppt bromine Oxide (BrO), respectively, by DOAS also at lower latitudes. These results intensified the discussion about the role of the RHS in the mid-latitude BL. Photochemical box model calculations show that the observed IO mixing ratios can destroy ~0.45 ppb ozone per hour. This is comparable to the rates of the known O_3-loss processes in the boundary layer. The model studies also reveal that IO, at these levels, has a strong influence on the BL photochemistry, increasing the OH/HO_2- and the NO_2/NO - ratios. In combination these changes lead to a reduction of the photochemical ozone formation, which - in addition - reduces ozone mixing ratios by up to 0.15 ppb/h. The studies for the Dead Sea case give no information on the heterogeneous process responsible for the bromine release, but they show that a total of 2 – 4 ppb of total bromine have to be released to explain the observed complete depletion of 60 ppb ozone in 2 – 3 hours.

  • Iodine Oxide in the marine boundary layer
    Nature, 1999
    Co-Authors: Björn Alicke, Kai Hebestreit, Jochen Stutz, Ulrich Platt
    Abstract:

    A striking example of the influence of halogen chemistry on tropospheric ozone levels is the episodic destruction of boundary-layer ozone during the Arctic sunrise by reactive halogen species^ 1 , ^ 2 . We detected Iodine Oxide in the boundary layer at Mace Head, Ireland (53°20′ N, 9°54′ W) during May 1997, which indicates that Iodine chemistry is occurring in the troposphere.

Thorsten Hoffmann - One of the best experts on this subject based on the ideXlab platform.

  • Observations of high concentrations of I2 and IO in coastal air supporting Iodine‐Oxide driven coastal new particle formation
    Geophysical Research Letters, 2010
    Co-Authors: Ru-jin Huang, Ulrich Platt, K. Seitz, T. Neary, Colin D. O'dowd, Thorsten Hoffmann
    Abstract:

    [1] Theoretical studies have predicted that concentrations of gaseous I2 and IO of the order of 80–100 ppt and 40–50 ppt, respectively, are required in coastal air to account for photochemically-driven coastal new-particle formation events to occur. However, measurements reported to date (i.e., ∼20 ppt I2, ≤ 10 ppt IO) have not supported the required model predictions. Here, we present measurements of high concentrations of I2 and IO in N.E. Atlantic marine air on the west coast of Ireland. The maximum mixing ratios of daytime I2 and IO over the seaweed beds during low tide were 302 ppt and 35 ppt, respectively. The I2 distribution was rather inhomogeneous, even at the inter-tidal zone, but closely related to the macroalgae biomass abundance. New particle formation bursts were frequently observed during daytime hours with the concentrations up to 4.5 × 105 particles cm−3 during low-tide conditions, and the concentrations of ultra-fine particles were positively correlated with the IO concentrations. Considering the constraints set out in theoretical studies for new particle formation via condensation of condensable Iodine Oxide vapours, the results reported here clearly demonstrate that the molecular Iodine and Iodine monOxide concentrations in coastal air are sufficient to meet the theoretical precursor concentrations required to drive intensive coastal new-particle formation from higher order condensable Iodine Oxides.

  • observations of high concentrations of i2 and io in coastal air supporting Iodine Oxide driven coastal new particle formation
    Geophysical Research Letters, 2010
    Co-Authors: Ru-jin Huang, Colin D Odowd, K. Seitz, T. Neary, U Platt, Thorsten Hoffmann
    Abstract:

    [1] Theoretical studies have predicted that concentrations of gaseous I2 and IO of the order of 80–100 ppt and 40–50 ppt, respectively, are required in coastal air to account for photochemically-driven coastal new-particle formation events to occur. However, measurements reported to date (i.e., ∼20 ppt I2, ≤ 10 ppt IO) have not supported the required model predictions. Here, we present measurements of high concentrations of I2 and IO in N.E. Atlantic marine air on the west coast of Ireland. The maximum mixing ratios of daytime I2 and IO over the seaweed beds during low tide were 302 ppt and 35 ppt, respectively. The I2 distribution was rather inhomogeneous, even at the inter-tidal zone, but closely related to the macroalgae biomass abundance. New particle formation bursts were frequently observed during daytime hours with the concentrations up to 4.5 × 105 particles cm−3 during low-tide conditions, and the concentrations of ultra-fine particles were positively correlated with the IO concentrations. Considering the constraints set out in theoretical studies for new particle formation via condensation of condensable Iodine Oxide vapours, the results reported here clearly demonstrate that the molecular Iodine and Iodine monOxide concentrations in coastal air are sufficient to meet the theoretical precursor concentrations required to drive intensive coastal new-particle formation from higher order condensable Iodine Oxides.

  • atmospheric science marine aerosols and Iodine emissions reply
    Nature, 2005
    Co-Authors: Colin D Odowd, Kaarle Hameri, Gerard S Jennings, Roya Bahreini, Liisa Pirjola, Markku Kulmala, Richard C. Flagan, John H. Seinfeld, Jose L Jimenez, Thorsten Hoffmann
    Abstract:

    O'Dowd et al. reply - McFiggans raises some interesting, but partly speculative, issues about the possibility of additional condensable-Iodine-vapour (CIV) precursors being involved in marine aerosol formation from biogenic Iodine emissions, and about the relative roles of Iodine Oxide and sulphuric acid in the marine new-particle formation process.

  • Marine aerosols and Iodine emissions (Reply)
    Nature, 2005
    Co-Authors: Colin D. O'dowd, Kaarle Hameri, Roya Bahreini, Liisa Pirjola, Markku Kulmala, Richard C. Flagan, John H. Seinfeld, Jose L Jimenez, S. Gerard Jennings, Thorsten Hoffmann
    Abstract:

    O'Dowd et al . reply - McFiggans ^ 1 raises some interesting, but partly speculative, issues about the possibility of additional condensable-Iodine-vapour (CIV) precursors being involved in marine aerosol formation from biogenic Iodine emissions, and about the relative roles of Iodine Oxide and sulphuric acid in the marine new-particle formation process.

  • coastal new particle formation a review of the current state of the art
    Environmental Chemistry, 2005
    Co-Authors: Colin D Odowd, Thorsten Hoffmann
    Abstract:

    Environmental Context.Atmospheric aerosols play an important role in determining the earth’s radiative budget, climate change and air quality levels. Much effort has been spent on quantifying the impact of aerosols on climate change; however, the largest gap in our knowledge relates to quantifying natural aerosol systems and the new particle formation process associated with these systems. The marine aerosol system is of particular interest due to the 70% ocean coverage of the earth’s surface. Coastal new particle formation events are though to be more frequent and of stronger intensity compared with open ocean events and thus have been studied in detail to identify possible processes leading to open ocean new particle production. Abstract.New particle formation via secondary gas-to-particle conversion processes over the oceans is one of the main mechanisms controlling the marine aerosol number population; however, despite extensive effort over the years, this phenomenon is still not well quantified. Coastal new particle formation events are more frequent than open ocean events and consequently have been studied in greater detail. This review article summarizes the recent studies into coastal new particle formation events and summarizes the linkage of these events to Iodine emissions and ultimate particle formation via Iodine Oxide nucleation processes. The current state of knowledge may be summarized by concluding that, in general, coastal nucleation events are driven by biogenic emissions of Iodine vapours that undergo rapid chemical reactions to produce condensable Iodine Oxides leading to nucleation and growth of new particles. The primary source of the condensable Iodine vapours is thought to be molecular Iodine (I2). The role of Iodine Oxides in open-ocean new particle production still remains an open question and is the most pressing next step to undertake.

Lj Carpenter - One of the best experts on this subject based on the ideXlab platform.

  • Understanding Iodine Chemistry Over the Northern and Equatorial Indian Ocean
    'American Geophysical Union (AGU)', 2019
    Co-Authors: As Mahajan, Lj Carpenter, Tinel L., Hulswar S., Sarkar A., Chance R, Mali P, Prakash S, Pn Vinayachandran
    Abstract:

    Observations of halogen Oxides, ozone, meteorological parameters, and physical and biogeochemical water column measurements were made in the Indian Ocean and its marine boundary layer as a part of the Second International Indian Ocean Expedition (IIOE‐2). The expedition took place on board the oceanographic research vessel Sagar Nidhi during 4–22 December 2015 from Goa, India, to Port Louis, Mauritius. Observations of mixed layer depth, averaged temperature, salinity, and nitrate concentrations were used to calculate predicted iodide concentrations in the seawater. The inorganic Iodine ocean‐atmosphere flux (hypoiodous acid [HOI] and molecular Iodine [I2]) was computed using the predicted iodide concentrations, measured atmospheric ozone, and wind speed. Iodine Oxide (IO) mixing ratios peaked at 0.47 ± 0.29 pptv (parts per trillion by volume) in the remote open ocean environment. The estimated iodide concentrations and HOI and I2 fluxes peaked at 200/500 nM, 410/680 nmol·m−2·day−1, and 20/80 nmol·m−2·day−1, respectively, depending on the parameterization used. The calculated fluxes for HOI and I2 were higher closer to the Indian subcontinent; however, atmospheric IO was only observed above the detection limit in the remote open ocean environment. We use NO2 observations to show that titration of IO by NO2 is the main reason for this result. These observations show that inorganic Iodine fluxes and atmospheric IO show similar trends in the Indian Ocean marine boundary layer, but the impact of inorganic Iodine emissions on Iodine chemistry is buffered in elevated NOx environments, even though the estimated oceanic Iodine fluxes are higher

  • Iodines impact on tropospheric oxidants: a global model study in GEOS-Chem
    'Copernicus GmbH', 2016
    Co-Authors: Sherwen T, Lj Carpenter, Mj Evans, Sj Andrews, Rt Lidster, Tk Koenig, Volkamer R, Saiz-lopez A, Prados-roman C, As Mahajan
    Abstract:

    We present a global simulation of tropospheric Iodine chemistry within the GEOS-Chem chemical transport model. This includes organic and inorganic Iodine sources, standard gas-phase Iodine chemistry, and simplified higher Iodine Oxide (I2OX, X = 2, 3, 4) chemistry, photolysis, deposition, and parametrized heterogeneous reactions. In comparisons with recent Iodine Oxide (IO) observations, the simulation shows an average bias of  ∼ +90 % with available surface observations in the marine boundary layer (outside of polar regions), and of  ∼ +73 % within the free troposphere (350 hPa  

  • Iodine's impact on tropospheric oxidants: a global model study in GEOS-Chem
    Copernicus Publications, 2016
    Co-Authors: T. Sherwen, Lj Carpenter, Mj Evans, Sj Andrews, Rt Lidster, Tk Koenig, B. Dix, R. Sinreich
    Abstract:

    We present a global simulation of tropospheric Iodine chemistry within the GEOS-Chem chemical transport model. This includes organic and inorganic Iodine sources, standard gas-phase Iodine chemistry, and simplified higher Iodine Oxide (I2OX, X = 2, 3, 4) chemistry, photolysis, deposition, and parametrized heterogeneous reactions. In comparisons with recent Iodine Oxide (IO) observations, the simulation shows an average bias of  ∼ +90 % with available surface observations in the marine boundary layer (outside of polar regions), and of  ∼ +73 % within the free troposphere (350 hPa  <  p  <  900 hPa) over the eastern Pacific. Iodine emissions (3.8 Tg yr−1) are overwhelmingly dominated by the inorganic ocean source, with 76 % of this emission from hypoiodous acid (HOI). HOI is also found to be the dominant Iodine species in terms of global tropospheric IY burden (contributing up to 70 %). The Iodine chemistry leads to a significant global tropospheric O3 burden decrease (9.0 %) compared to standard GEOS-Chem (v9-2). The Iodine-driven OX loss rate1 (748 Tg OX yr−1) is due to photolysis of HOI (78 %), photolysis of OIO (21 %), and reaction between IO and BrO (1 %). Increases in global mean OH concentrations (1.8 %) by increased conversion of hydroperoxy radicals exceeds the decrease in OH primary production from the reduced O3 concentration. We perform sensitivity studies on a range of parameters and conclude that the simulation is sensitive to choices in parametrization of heterogeneous uptake, ocean surface iodide, and I2OX (X = 2, 3, 4) photolysis. The new Iodine chemistry combines with previously implemented bromine chemistry to yield a total bromine- and Iodine-driven tropospheric O3 burden decrease of 14.4 % compared to a simulation without Iodine and bromine chemistry in the model, and a small increase in OH (1.8 %). This is a significant impact and so halogen chemistry needs to be considered in both climate and air quality models. 1 Here OX is defined as O3 + NO2 + 2NO3 + PAN + PMN+PPN + HNO4 + 3N2O5 + HNO3 + BrO + HOBr + BrNO2+2BrNO3 + MPN + IO + HOI + INO2 + 2INO3 + 2OIO+2I2O2 + 3I2O3 + 4I2O4, where PAN  =  peroxyacetyl nitrate, PPN  =  peroxypropionyl nitrate, MPN  =  methyl peroxy nitrate, and MPN  =  peroxymethacryloyl nitrate

  • Atmospheric Iodine levels influenced by sea surface emissions of inorganic Iodine
    'Springer Science and Business Media LLC', 2013
    Co-Authors: Lj Carpenter, Parthipan R, Wilson J, Sm Macdonald, Kumar R, Rw Saunders, Plane Jmc
    Abstract:

    Naturally occurring bromine- and Iodine-containing compounds substantially reduce regional, and possibly even global, tropospheric ozone levels. As such, these halogen gases reduce the global warming effects of ozone in the troposphere, and its capacity to initiate the chemical removal of hydrocarbons such as methane. The majority of halogen-related surface ozone destruction is attributable to Iodine chemistry. So far, organic Iodine compounds have been assumed to serve as the main source of oceanic Iodine emissions. However, known organic sources of atmospheric Iodine cannot account for gas-phase Iodine Oxide concentrations in the lower troposphere over the tropical oceans. Here, we quantify gaseous emissions of inorganic Iodine following the reaction of iodide with ozone in a series of laboratory experiments. We show that the reaction of iodide with ozone leads to the formation of both molecular Iodine and hypoiodous acid. Using a kinetic box model of the sea surface layer and a one-dimensional model of the marine boundary layer, we show that the reaction of ozone with iodide on the sea surface could account for around 75% of observed Iodine Oxide levels over the tropical Atlantic Ocean. According to the sea surface model, hypoiodous acid - not previously considered as an oceanic source of Iodine - is emitted at a rate ten-fold higher than that of molecular Iodine under ambient conditions

  • Coastal zone production of IO precursors: a 2-dimensional study
    Atmospheric Chemistry and Physics, 2001
    Co-Authors: Lj Carpenter, U Platt, K. Hebestreit, P. S. Liss
    Abstract:

    At Mace Head, Eire, in the coastal East Atlantic, diiodomethane has been identified as an important precursor of Iodine Oxide radicals. Peak concentrations of both CH2I2 and IO at low water indicate that the intertidal region is a strong source of organo-Iodines. Atmospheric measurements of CH2I2 made in marine air are compared with the concentrations predicted by a 2-dimensional model incorporating horizontal and vertical dispersion of surface emissions. The model shows that micrometeorological variability, proximity of the site to emissions, and photolysis all play important roles in determining the CH2I2 concentrations at Mace Head. In addition to a tidal-height dependent intertidal flux, which was estimated from seaweed production data, a contribution from offshore (non-local) sources was required in order to reproduce the strong signature of photolysis in the CH2I2 observations. A combination of an offshore flux and an intertidal flux (of up to 1.4 × 109 molecules cm-2s-1 at low water) results in good agreement between the measured and modelled CH2I2 concentrations. Although this study does not necessarily infer emission of CH2I2 from the open ocean, it suggests that air-sea exchange of CH2I2 in coastal waters does occur.