The Experts below are selected from a list of 45 Experts worldwide ranked by ideXlab platform
John M. C. Plane - One of the best experts on this subject based on the ideXlab platform.
-
Photochemistry of OIO: Laboratory study and atmospheric implications
Geophysical Research Letters, 2009Co-Authors: Juan Carlos Gómez Martín, Stephen H. Ashworth, Anoop S. Mahajan, John M. C. PlaneAbstract:[1] Iodine chemistry influences the oxidizing capacity of the atmosphere, principally by depleting ozone, and induces the formation of new particles in the marine boundary layer. The photochemistry of Iodine Dioxide (OIO) plays a key role in both these processes. Here we report that OIO photolyses in the visible (480–650 nm), yielding Iodine atoms with a quantum efficiency of unity (1.07 ± 0.15). As a result, much smaller sources of Iodine precursors are required to cause significant ozone depletion, which has important implications for the marine boundary layer ozone budget.
-
High resolution spectroscopy of the OIO radical: Implications for the ozone-depleting potential of Iodine
Geophysical Research Letters, 2002Co-Authors: Stephen H. Ashworth, Beverley J. Allan, John M. C. PlaneAbstract:The absorption spectrum of Iodine Dioxide (OIO), obtained at high resolution between 540 and 605 nm by cavity ring-down spectroscopy, exhibits no evidence of coarse rotational structure. Furthermore, a laser induced fluorescence spectrum was not observed when pumping the molecule in this region of the visible spectrum. Ab initio quantum calculations were performed on the ground and first excited states of OIO. The rotational envelopes of the observed absorption bands are very satisfactorily simulated if the lifetime of the excited state is 200 ± 50 fs, indicating prompt predissociation. Quantum calculations indicate photolysis to I + O2, rather than O + IO. The estimated photodissociation rate of OIO in daylight ranges from 0.36 to 2.2 s-1, depending on the choice of absolute cross-section, which explains why OIO has only been observed in the atmosphere after sunset. Photolysis to yield atomic I will enhance the O3-depleting potential of Iodine in the remote marine boundary layer
-
Observations of OIO in the remote marine boundary layer
Geophysical Research Letters, 2001Co-Authors: B. J. Allan, John M. C. Plane, Gordon McfiggansAbstract:We report observations of Iodine Dioxide (OIO) in the remote marine boundary layer. The measurements were made at the remote site of Cape Grim in Tasmania, using the technique of differential optical absorption spectroscopy (DOAS), in the 540–570 nm spectral region. Employing a cross-section of 6.8 × 10−17 cm² at 548.6 nm, the concentration of OIO was found to vary from below the detection limit of the instrument (≈ 0.5 parts per trillion (ppt)) to a maximum of almost 3 ppt after sunset. During the day the upper limit to the atmospheric turnover time of OIO was found to be 20 min., when removal by gas-phase reaction and/or photolysis appears to dominate. At night the much longer turnover time of ≈ 1–4 hours can be explained by uptake on aerosol.
Gordon Mcfiggans - One of the best experts on this subject based on the ideXlab platform.
-
Iodine Dioxide nucleation simulations in coastal and remote marine environments
Journal of Geophysical Research, 2009Co-Authors: Henri Vuollekoski, Veli-matti Kerminen, Tatu Anttila, S.-l. Sihto, Hannele Korhonen, Gordon Mcfiggans, Colin D. O'dowd, Marko Vana, Mikael Ehn, Markku KulmalaAbstract:[1] Aerosol dynamical box model simulations of coastal new particle formation were performed in order to investigate the nucleation and growth mechanisms in this environment. In the simulations the nucleating vapor was assumed to be Iodine Dioxide (OIO). Both Eulerian and Lagrangian type simulations were made and compared with observations. We tested three nucleation mechanisms: kinetic nucleation of OIO (K × [OIO]2), activation of clusters by OIO (A × [OIO]) and sulphuric acid-induced activation of clusters containing OIO (B × [OIO] × [H2SO4]). All the nucleation mechanisms provided reasonable results, although the growth of particles due to condensation is inadequate in kinetic nucleation cases as compared with experimental measurements. Growth of newly formed particles could be assisted by any low-volatility vapors should their concentration exceed 109 cm−3. Using the obtained values of coefficients K, A, and B we found that nucleation driven by Iodine compounds in remote marine areas is possible, but by OIO and H2SO4 alone, only a minor fraction of newly formed particles is likely to reach detectable sizes. Owing to the scavenging by coagulation with background aerosol particles, few of them will likely reach climatically relevant sizes by acting as seed particles for other low-volatility vapors. In order to elucidate the significance of our results, more detailed measurements of OIO source and photolysis rates, dimensions of precursor areas, and particle chemical composition are needed.
-
Simulations of Iodine Dioxide Nucleation
Nucleation and Atmospheric Aerosols, 2007Co-Authors: Henri Vuollekoski, Markku Kulmala, Veli-matti Kerminen, Tatu Anttila, S.-l. Sihto, Ilona Riipinen, Hannele Korhonen, Gordon Mcfiggans, Colin D. O'dowdAbstract:Aerosol dynamical simulations of coastal new particle formation have been performed in order to investigate the nucleation and growth mechanisms in this environment. In the simulations, it is assumed that the nucleating vapour is Iodine Dioxide. Both Eulerian and Lagrangian type simulations have been performed and compared to observations. We have found it difficult to achieve the observed, enormous growth rates, and simulations agree with the experiments only when OIO concentration is very high and growth time has been prolonged
-
Observations of OIO in the remote marine boundary layer
Geophysical Research Letters, 2001Co-Authors: B. J. Allan, John M. C. Plane, Gordon McfiggansAbstract:We report observations of Iodine Dioxide (OIO) in the remote marine boundary layer. The measurements were made at the remote site of Cape Grim in Tasmania, using the technique of differential optical absorption spectroscopy (DOAS), in the 540–570 nm spectral region. Employing a cross-section of 6.8 × 10−17 cm² at 548.6 nm, the concentration of OIO was found to vary from below the detection limit of the instrument (≈ 0.5 parts per trillion (ppt)) to a maximum of almost 3 ppt after sunset. During the day the upper limit to the atmospheric turnover time of OIO was found to be 20 min., when removal by gas-phase reaction and/or photolysis appears to dominate. At night the much longer turnover time of ≈ 1–4 hours can be explained by uptake on aerosol.
Markku Kulmala - One of the best experts on this subject based on the ideXlab platform.
-
Iodine Dioxide nucleation simulations in coastal and remote marine environments
Journal of Geophysical Research, 2009Co-Authors: Henri Vuollekoski, Veli-matti Kerminen, Tatu Anttila, S.-l. Sihto, Hannele Korhonen, Gordon Mcfiggans, Colin D. O'dowd, Marko Vana, Mikael Ehn, Markku KulmalaAbstract:[1] Aerosol dynamical box model simulations of coastal new particle formation were performed in order to investigate the nucleation and growth mechanisms in this environment. In the simulations the nucleating vapor was assumed to be Iodine Dioxide (OIO). Both Eulerian and Lagrangian type simulations were made and compared with observations. We tested three nucleation mechanisms: kinetic nucleation of OIO (K × [OIO]2), activation of clusters by OIO (A × [OIO]) and sulphuric acid-induced activation of clusters containing OIO (B × [OIO] × [H2SO4]). All the nucleation mechanisms provided reasonable results, although the growth of particles due to condensation is inadequate in kinetic nucleation cases as compared with experimental measurements. Growth of newly formed particles could be assisted by any low-volatility vapors should their concentration exceed 109 cm−3. Using the obtained values of coefficients K, A, and B we found that nucleation driven by Iodine compounds in remote marine areas is possible, but by OIO and H2SO4 alone, only a minor fraction of newly formed particles is likely to reach detectable sizes. Owing to the scavenging by coagulation with background aerosol particles, few of them will likely reach climatically relevant sizes by acting as seed particles for other low-volatility vapors. In order to elucidate the significance of our results, more detailed measurements of OIO source and photolysis rates, dimensions of precursor areas, and particle chemical composition are needed.
-
Simulations of Iodine Dioxide Nucleation
Nucleation and Atmospheric Aerosols, 2007Co-Authors: Henri Vuollekoski, Markku Kulmala, Veli-matti Kerminen, Tatu Anttila, S.-l. Sihto, Ilona Riipinen, Hannele Korhonen, Gordon Mcfiggans, Colin D. O'dowdAbstract:Aerosol dynamical simulations of coastal new particle formation have been performed in order to investigate the nucleation and growth mechanisms in this environment. In the simulations, it is assumed that the nucleating vapour is Iodine Dioxide. Both Eulerian and Lagrangian type simulations have been performed and compared to observations. We have found it difficult to achieve the observed, enormous growth rates, and simulations agree with the experiments only when OIO concentration is very high and growth time has been prolonged
-
OIO nucleation simulations
2007Co-Authors: Henri Vuollekoski, Markku Kulmala, Ilona Riipinen, Hannu KorhonenAbstract:, 2005). The phenomenon overlaps with low tide, during which algae are exposed to ozone in air and emit Iodine vapours. Various chemical reactions result in large amounts of Iodine Dioxide (OIO) in the atmosphere, which is believed to be a nucleating vapour.We have simulated new particle formation with University of Helsinki Multi-component Aerosol model (UHMA, Korhonen
Juan Carlos Gómez Martín - One of the best experts on this subject based on the ideXlab platform.
-
Photochemistry of OIO: Laboratory study and atmospheric implications
Geophysical Research Letters, 2009Co-Authors: Juan Carlos Gómez Martín, Stephen H. Ashworth, Anoop S. Mahajan, John M. C. PlaneAbstract:[1] Iodine chemistry influences the oxidizing capacity of the atmosphere, principally by depleting ozone, and induces the formation of new particles in the marine boundary layer. The photochemistry of Iodine Dioxide (OIO) plays a key role in both these processes. Here we report that OIO photolyses in the visible (480–650 nm), yielding Iodine atoms with a quantum efficiency of unity (1.07 ± 0.15). As a result, much smaller sources of Iodine precursors are required to cause significant ozone depletion, which has important implications for the marine boundary layer ozone budget.
-
Spectroscopic studies of the I2/O3 photochemistry: Part 1: Determination of the absolute absorption cross sections of Iodine oxides of atmospheric relevance
Journal of Photochemistry and Photobiology A-chemistry, 2005Co-Authors: Juan Carlos Gómez Martín, Peter Spietz, John P. BurrowsAbstract:Abstract Multichannel time resolved absorption spectroscopy has been coupled with flash photolysis of mixtures of molecular Iodine and ozone to study the spectra and determine absorption cross sections of Iodine oxides. Simultaneously, the behaviour of the Iodine atoms has been measured by atomic resonance spectroscopy. To separate overlapping molecular absorptions, multivariate analysis techniques have been used to yield the optical density versus time curve at an optimal wavelength for each individual molecular absorber. After the initial photolysis of I2 and some O3, it is assumed that the number of Iodine atoms contained in the chemical system is invariant in time and that the individual optical densities of all the relevant species are observed. The solution of the resultant over-determined system of linear equations yields the absolute absorption cross sections of the Iodine containing molecular species: ground state Iodine monoxide, IO(X2Π3/2, ν″ = 0), vibrationally excited Iodine monoxide, IO(X2Π3/2, ν″ > 0), ground state Iodine Dioxide, OIO(2B1), and the spectra of three other Iodine oxides, some of which have been observed for the first time in this study. One of these oxides has been tentatively assigned to I2O2, and possible assignments of the other two have been discussed. The values of absolute absorption cross sections for selected vacuum wavelengths at 298 K were determined to be: σIO(4←0)(427.2 nm) = (3.5 ± 0.3) × 10−17 cm2, σIO(3←1)(459.3 nm) = (4.5 ± 0.5) × 10−17 cm2, σIO(1←2)(484.9 nm) = (6.0 ± 0.5) × 10−17 cm2, σOIO(0,5,1←0,0,0)(549.3 nm) = (1.3 ± 0.3) × 10−17 cm2 and for an up to now unidentified higher Iodine oxide σ(356 nm) ≥ (7.8 ± 1.2) × 10−19 cm2 × I atom−1. The spectral resolution of the resultant absorption cross sections is 0.12 nm FWHM in case of IO and 0.35 nm FWHM in case of OIO. Previous determinations of these absorption cross sections have been reviewed.
Stephen H. Ashworth - One of the best experts on this subject based on the ideXlab platform.
-
Photochemistry of OIO: Laboratory study and atmospheric implications
Geophysical Research Letters, 2009Co-Authors: Juan Carlos Gómez Martín, Stephen H. Ashworth, Anoop S. Mahajan, John M. C. PlaneAbstract:[1] Iodine chemistry influences the oxidizing capacity of the atmosphere, principally by depleting ozone, and induces the formation of new particles in the marine boundary layer. The photochemistry of Iodine Dioxide (OIO) plays a key role in both these processes. Here we report that OIO photolyses in the visible (480–650 nm), yielding Iodine atoms with a quantum efficiency of unity (1.07 ± 0.15). As a result, much smaller sources of Iodine precursors are required to cause significant ozone depletion, which has important implications for the marine boundary layer ozone budget.
-
High resolution spectroscopy of the OIO radical: Implications for the ozone-depleting potential of Iodine
Geophysical Research Letters, 2002Co-Authors: Stephen H. Ashworth, Beverley J. Allan, John M. C. PlaneAbstract:The absorption spectrum of Iodine Dioxide (OIO), obtained at high resolution between 540 and 605 nm by cavity ring-down spectroscopy, exhibits no evidence of coarse rotational structure. Furthermore, a laser induced fluorescence spectrum was not observed when pumping the molecule in this region of the visible spectrum. Ab initio quantum calculations were performed on the ground and first excited states of OIO. The rotational envelopes of the observed absorption bands are very satisfactorily simulated if the lifetime of the excited state is 200 ± 50 fs, indicating prompt predissociation. Quantum calculations indicate photolysis to I + O2, rather than O + IO. The estimated photodissociation rate of OIO in daylight ranges from 0.36 to 2.2 s-1, depending on the choice of absolute cross-section, which explains why OIO has only been observed in the atmosphere after sunset. Photolysis to yield atomic I will enhance the O3-depleting potential of Iodine in the remote marine boundary layer