Iodine Chemistry and its Role in Halogen Activation and Ozone Loss in the Marine Boundary Layer: A Model Study

A detailed set of reactions treating the gas and aqueous phase chemistry of the most important iodine species in the marine boundary layer (MBL) has been added to a box model which describes Br and Cl chemistry in the MBL. While Br and Cl originate from seasalt, the I compounds are largely derived photochemically from several biogenic alkyl iodides, in particular CH2I2, CH2ClI, C2H5I, C3H7I, or CH3I which are released from the sea. Their photodissociation produces some inorganic iodine gases which can rapidly react in the gas and aqueous phase with other halogen compounds. Scavenging of the iodine species HI, HOI, INO2, and IONO2 by aerosol particles is not a permanent sink as assumed in previous modeling studies. Aqueous-phase chemical reactions can produce the compounds IBr, ICl, and I2, which will be released back into the gas phase due to their low solubility. Our study, although highly theoretical, suggests that almost all particulate iodine is in the chemical form of IO-3. Other aqueous-phase species are only temporary reservoirs and can be re-activated to yield gas phase iodine. Assuming release rates of the organic iodine compounds which yield atmospheric concentrations similar to some measurements, we calculate significant concentrations of reactive halogen gases. The addition of iodine chemistry to our reaction scheme has the effect of accelerating photochemical Br and Cl release from the seasalt. This causes an enhancement in ozone destruction rates in the MBL over that arising from the well established reactions O(1D) + H2O → 2OH, HO2 + O3 → OH + 2O2, and OH + O3 → HO2 + O2. The given reaction scheme accounts for the formation of particulate iodine which is preferably accumulated in the smaller sulfate aerosol particles.

[1]  Y. Bedjanian,et al.  Kinetics and Mechanism of the IO + ClO Reaction , 1997 .

[2]  R. Duce,et al.  Gaseous and particulate iodine in the marine atmosphere , 1972 .

[3]  P. G. Hill,et al.  A Fundamental Equation of State for Heavy Water , 1982 .

[4]  R. A. Cox,et al.  Photochemical aspects of tropospheric iodine behaviour , 1985 .

[5]  Paul J. Crutzen,et al.  On the disproportionate role of tropospheric ozone as a filter against solar UV‐B radiation , 1989 .

[6]  G. Poulet,et al.  The BrO + Ch3O2 reaction: Kinetics and role in the atmospheric ozone budget , 1997 .

[7]  P. Mirabel,et al.  INVESTIGATION OF THE UPTAKE RATE OF OZONE AND METHYL HYDROPEROXIDE BY WATER SURFACES , 1997 .

[8]  Krishan Kumar,et al.  Non-Metal Redox Kinetics: Oxidation of Iodide by Hypochlorous Acid and by Nitrogen Trichloride Measured by the Pulsed-Accelerated-Flow Method. , 1988 .

[9]  I. Epstein,et al.  RATE CONSTANTS FOR REACTIONS BETWEEN IODINE- AND CHLORINE-CONTAINING SPECIES : A DETAILED MECHANISM OF THE CHLORINE DIOXIDE/CHLORITE-IODIDE REACTION , 1996 .

[10]  R. Cicerone.  Halogens in the atmosphere , 1981 .

[11]  Rohith Gunawardena.  Atmospheric methyl iodide , 1985 .

[12]  R. Garcia,et al.  On the role of iodine in ozone depletion , 1994 .

[13]  D. W. Margerum,et al.  Non‐Metal Redox Kinetics: Hypobromite and Hypobromous Acid Reactions with Iodide and with Sulfite and the Hydrolysis of Bromosulfate. , 1991 .

[14]  Douglas D. Davis,et al.  Potential impact of iodine on tropospheric levels of ozone and other critical oxidants , 1996 .

[15]  M. Kritz,et al.  Diurnal fluctuations of Br and I in the tropical marine atmosphere , 1980 .

[16]  Manfred Eigen,et al.  The Kinetics of Halogen Hydrolysis , 1962 .

[17]  Dale W. Margerum,et al.  Kinetics of hydrolysis of iodine monochloride measured by the pulsed-accelerated-flow method , 1989 .

[18]  K. Heumann,et al.  Determinations of methyl iodide in the Antarctic atmosphere and the South Polar Sea , 1992 .

[19]  P. Crutzen,et al.  Temperature dependence of UV absorption cross sections and atmospheric implications of several alkyl iodides , 1997 .

[20]  V. Truesdale.  KINETICS OF DISPROPORTIONATION OF HYPOIODOUS ACID AT HIGH PH, WITH AN EXTRAPOLATION TO RAINWATER , 1997 .

[21]  P. Crutzen,et al.  Are there interactions of iodine and sulfur species in marine air photochemistry , 1990 .

[22]  Irving R. Epstein,et al.  Bifurcation analysis of chemical reaction mechanisms. I, Steady state bifurcation structure , 1991 .

[23]  K. Heumann,et al.  Iodine speciation in size fractionated atmospheric particles by isotope dilution mass spectrometry , 1995, Analytical and bioanalytical chemistry.

[24]  R. Wayne,et al.  Inorganic gas-phase reactions of the nitrate radical: iodine + nitrate radical and iodine atom + nitrate radical , 1992 .

[25]  D. D. Wagman,et al.  The NBS tables of chemical thermodynamic properties : selected values for inorganic and C1 and C2 organic substances in SI units , 1982 .

[26]  D. W. Margerum,et al.  Non-metal redox kinetics: iodine monobromide reaction with iodide ion and the hydrolysis of IBr , 1991 .

[27]  D. W. Margerum,et al.  Non-metal redox kinetics: hypobromite and hypobromous acid reactions with iodide and with sulfite and the hydrolysis of bromosulfate , 1991 .

[28]  R. H. Simoyi,et al.  Kinetics and Mechanism of the Complex Bromate−Iodine Reaction1 , 1996 .

[29]  M. Kurylo,et al.  Absorption cross sections, kinetics of formation, and self-reaction of the IO radical produced via the laser photolysis of N2O/I2/N2 mixtures , 1995 .

[30]  J. Tellinghuisen.  Resolution of the visible‐infrared absorption spectrum of I2 into three contributing transitions , 1973 .

[31]  I. Epstein,et al.  Systematic design of chemical oscillators. 43. Mechanistic study of a coupled chemical oscillator: the bromate-chlorite-iodide reaction , 1988 .

[32]  D. Seery,et al.  The Continuous Absorption Spectra of Chlorine, Bromine, Bromine Chloride, Iodine Chloride, and Iodine Bromide , 1964 .

[33]  M. Khalil,et al.  Atmospheric methyl iodide (CH3I) , 1982 .

[34]  R. Wayne,et al.  Inorganic Gas-Phase Reactions of the Nitrate Radical: I2 + NO3 and I + NO3. , 1992 .

[35]  A. Ravishankara,et al.  Absorption Cross Sections and Self-Reaction Kinetics of the IO Radical , 1997 .

[36]  R. Garcia,et al.  Ozone depletion and global warming potentials of CF3I , 1994 .

[37]  J. Crowley,et al.  Ultraviolet—Visible Absorption Cross Sections of Gaseous HOI and Its Photolysis at 355 nm. , 1998 .

[38]  D. Murphy,et al.  Bromine, iodine, and chlorine in single aerosol particles at Cape Grim , 1997 .

[39]  K. Heumann,et al.  GC determination of volatile organoiodine and organobromine compounds in Arctic seawater and air samples , 1993 .

[40]  R. Duce,et al.  Tropospheric Halogen Gases: Inorganic and Organic Components , 1976, Science.

[41]  K. Ballschmiter,et al.  Chemistry of organic traces in air , 1986 .

[42]  Douglas D. Davis,et al.  Iodine - Its possible role in tropospheric photochemistry , 1980 .

[43]  Y. Muramatsu,et al.  Determination of organic, inorganic and particulate iodine in the coastal atmosphere of Japan , 1995 .

[44]  S. Furrow.  Reactions of iodine intermediates in iodate-hydrogen peroxide oscillators , 1987 .

[45]  Paul J. Crutzen,et al.  Model study indicating halogen activation and ozone destruction in polluted air masses transported to the sea , 1996 .

[46]  P. Crutzen,et al.  A mechanism for halogen release from sea-salt aerosol in the remote marine boundary layer , 1996, Nature.

[47]  M. Molina,et al.  Chemical kinetics and photochemical data for use in stratospheric modeling , 1985 .

[48]  Krishan Kumar,et al.  Nonmetal redox kinetics: oxidation of iodide by hypochlorous acid and by nitrogen trichloride measured by the pulsed-accelerated-flow method , 1988 .

[49]  H. Singh,et al.  Methyl halides in and over the eastern Pacific (40°N–32°S) , 1983 .

[50]  R. Mesmer,et al.  The hydrolysis of iodine: Equilibria at high temperatures , 1985 .