Direct evidence for coastal iodine particles from Laminaria macroalgae – linkage to emissions of molecular iodine

Renewal of ultrafine aerosols in the marine boundary layer may lead to repopulation of the marine distribution and ultimately determine the concentration of cloud condensation nuclei (CCN). Thus the formation of nanometre-scale particles can lead to enhanced scattering of incoming radiation and a net cooling of the atmosphere. The recent demonstration of the chamber formation of new particles from the photolytic production of condensable iodine-containing compounds from diiodomethane (CH2I2), (O'Dowd et al., 2002; Kolb, 2002; Jimenez et al., 2003a; Burkholder and Ravishankara, 2003), provides an additional mechanism to the gas-to-particle conversion of sulphuric acid formed in the photo-oxidation of dimethylsulphide for marine aerosol repopulation. CH2I2 is emitted from seaweeds (Carpenter et al., 1999, 2000) and has been suggested as an initiator of particle formation. We demonstrate here for the first time that ultrafine iodine-containing particles are produced by intertidal macroalgae exposed to ambient levels of ozone. The particle composition is very similar both to those formed in the chamber photo-oxidation of diiodomethane and in the oxidation of molecular iodine by ozone. The particles formed in all three systems are similarly aspherical. When small, those formed in the molecular iodine system swell only moderately when exposed to increased humidity environments, and swell progressively less with increasing size; this behaviour occurs whether they are formed in dry or humid environments, in contrast to those in the CH2I2 system. Direct coastal boundary layer observations of molecular iodine, ultrafine particle production and iodocarbons are reported. Using a newly measured molecular iodine photolysis rate, it is shown that, if atomic iodine is involved in the observed particle bursts, it is of the order of at least 1000 times more likely to result from molecular iodine photolysis than diiodomethane photolysis. A hypothesis for molecular iodine release from intertidal macroalgae is presented and the potential importance of macroalgal iodine particles in their contribution to CCN and global radiative forcing are discussed.

[1]  D. Rader,et al.  Application of the tandem differential mobility analyzer to studies of droplet growth or evaporation , 1986 .

[2]  U. Tapper,et al.  Biogenic iodine emissions and identification of end-products in coastal ultrafine particles during nucleation bursts , 2002 .

[3]  J. Plane,et al.  Absolute absorption cross-section and photolysis rate of I 2 , 2004 .

[4]  A. Berner,et al.  A new electromobility spectrometer for the measurement of aerosol size distributions in the size range from 1 to 1000 nm , 1991 .

[5]  J. R. Koch,et al.  Ozone: a tool for probing programmed cell death in plants , 2000, Plant Molecular Biology.

[6]  A. C. Vikis,et al.  Raman spectra of iodine oxyacids produced by the gas-phase reaction of iodine with ozone in the presence of water vapour , 1987 .

[7]  Clive D Rodgers,et al.  Inverse Methods for Atmospheric Sounding: Theory and Practice , 2000 .

[8]  Charles E. Kolb,et al.  A Numerical Characterization of Particle Beam Collimation by an Aerodynamic Lens-Nozzle System: Part I. An Individual Lens or Nozzle , 2002 .

[9]  Kenneth A. Smith,et al.  Development of an Aerosol Mass Spectrometer for Size and Composition Analysis of Submicron Particles , 2000 .

[10]  C. O'Dowd,et al.  On the photochemical production of new particles in the coastal boundary layer , 1999 .

[11]  D. Worsnop,et al.  Correction to Quantitative sampling using an Aerodyne aerosol mass spectrometer: 1. Techniques of d , 2003 .

[12]  Ulrich Platt,et al.  Short‐lived alkyl iodides and bromides at Mace Head, Ireland: Links to biogenic sources and halogen oxide production , 1999 .

[13]  Liisa Pirjola,et al.  Can new particle formation occur in the clean marine boundary layer , 2000 .

[14]  G. Luther,et al.  Molecular iodine reduction in seawater: an improved rate equation considering organic compounds , 1995 .

[15]  C. N. Hewitt,et al.  A dedicated study of new particle formation and fate in the coastal environment (PARFORCE): overview of objectives and achievements , 2002 .

[16]  B. Kloareg,et al.  Iodine uptake in Laminariales involves extracellular, haloperoxidase-mediated oxidation of iodide , 1998, Planta.

[17]  E. Rabinowitch,et al.  Dissociation of Excited Iodine Molecules , 1936 .

[18]  M. Väkevä,et al.  Hygroscopic properties of nucleation mode and Aitken mode particles during nucleation bursts and in background air on the west coast of Ireland , 2002 .

[19]  Appendix A : New Particle Formation from Photooxidation of Diiodomethane ( CH 2 I 2 ) * , 2003 .

[20]  P. Monks,et al.  Performance of a single-monochromator diode array spectroradiometer for the determination of actinic flux and atmospheric photolysis frequencies , 2003 .

[21]  J. C. Wren,et al.  Raman spectra of I4O9 formed by the reaction of iodine with ozone , 1985 .

[22]  L. Brewer,et al.  Quantum Yield for Unimolecular Dissociation of I2 in Visible Absorption , 1972 .

[23]  G. Mcfiggans,et al.  A modeling study of iodine chemistry in the marine boundary layer , 2000 .

[24]  J. Seinfeld,et al.  Marine aerosol formation from biogenic iodine emissions , 2002, Nature.

[25]  C. Kolb.  Atmospheric chemistry: Iodine's air of importance , 2002, Nature.

[26]  P. Liss,et al.  Novel biogenic iodine‐containing trihalomethanes and other short‐lived halocarbons in the coastal east Atlantic , 2000 .

[27]  A. C. Vikis,et al.  Reaction of iodine with ozone in the gas phase , 1985 .

[28]  Charles E. Kolb,et al.  Ambient aerosol sampling using the Aerodyne Aerosol Mass Spectrometer , 2003 .

[29]  G. Mcfiggans,et al.  Observations of OIO in the remote marine boundary layer , 2001 .

[30]  Hugh Coe,et al.  Quantitative sampling using an Aerodyne aerosol mass spectrometer 1. Techniques of data interpretation and error analysis , 2003 .

[31]  J. Plane,et al.  Novel iodine chemistry in the marine boundary layer , 2004 .

[32]  A. Ravishankara,et al.  Laboratory studies of the homogeneous nucleation of iodine oxides , 2003 .

[33]  J. Seinfeld,et al.  New particle formation from photooxidation of diiodomethane (CH2I2) , 2003 .