title: Coastal iodine emissions: part 2. Chamber experiments of particle formation from Laminaria digitata-derived and laboratory-generated I₂.
abstract: Laboratory studies into particle formation from Laminaria digitata macroalgae were undertaken to elucidate aerosol formation for a range of I(2) (0.3-76 ppb(v)) and O(3) (<3-96 ppb(v)) mixing ratios and light levels (E(PAR) = 15, 100, and 235 μmol photons m(-2) s(-1)). No clear pattern was observed for I(2) or aerosol parameters as a function of light levels. Aerosol mass fluxes and particle number concentrations, were, however, correlated with I(2) mixing ratios for low O(3) mixing ratios of <3 ppb(v) (R(2) = 0.7 and 0.83, respectively for low light levels, and R(2) = 0.95 and 0.98, respectively for medium light levels). Additional experiments into particle production as a function of laboratory-generated I(2), over a mixing ratio range of 1-8 ppb(v), were conducted under moderate O(3) mixing ratios (∼24 ppb(v)) where a clear, 100-fold or greater, increase in the aerosol number concentrations and mass fluxes was observed compared to the low O(3) experiments. A linear relationship between particle concentration and I(2) was found, in reasonable agreement with previous studies. Scaling the laboratory relationship to aerosol concentrations typical of the coastal boundary layer suggests a I(2) mixing ratio range of 6-93 ppt(v) can account for the observed particle production events. Aerosol number concentration produced from I(2) is more than a factor of 10 higher than that produced from CH(2)I(2) for the same mixing ratios.
authors.affiliation: School of Physics and Centre for Climate & Air Pollution Studies, Ryan Institute, National University of Ireland Galway, University Road, Galway, Ireland.
authors.forename: Ciaran
authors.initials: C
authors.lastname: Monahan
authors.forename: Enowmbi R
authors.initials: ER
authors.lastname: Ashu-Ayem
authors.forename: Udo
authors.initials: U
authors.lastname: Nitschke
authors.forename: Steven B
authors.initials: SB
authors.lastname: Darby
authors.forename: Paul D
authors.initials: PD
authors.lastname: Smith
authors.forename: Dagmar B
authors.initials: DB
authors.lastname: Stengel
authors.forename: Dean S
authors.initials: DS
authors.lastname: Venables
authors.forename: Colin D
authors.initials: CD
authors.lastname: O'Dowd
mesh_terms: D000336:Aerosols / Q000032:analysis / Q000737:chemistry; D000393:Air Pollutants / Q000032:analysis; D007455:Iodine; D044423:Kelp; D007795:Laminaria / Q000502:physiology*; D008027:Light; D008386:Marine Biology / Q000379:methods*; D010126:Ozone
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D010126:Ozone; D007455:Iodine