Laboratory studies into particle formation from
Laminaria digitata macroalgae were undertaken to elucidate
aerosol formation for a range of I2 (0.3−76 ppbv) and O3
(<3−96 ppbv) mixing ratios and light levels (EPAR = 15, 100,
and 235 μmol photons m−2 s−1). No clear pattern was
observed for I2 or aerosol parameters as a function of light
levels. Aerosol mass fluxes and particle number concentrations,
were, however, correlated with I2 mixing ratios for low O3
mixing ratios of <3 ppbv (R2 = 0.7 and 0.83, respectively for low light levels, and R2 = 0.95 and 0.98, respectively for medium light
levels). Additional experiments into particle production as a function of laboratory-generated I2, over a mixing ratio range of 1−8
ppbv, were conducted under moderate O3 mixing ratios (∼24 ppbv) where a clear, 100-fold or greater, increase in the aerosol
number concentrations and mass fluxes was observed compared to the low O3 experiments. A linear relationship between particle
concentration and I2 was found, in reasonable agreement with previous studies. Scaling the laboratory relationship to aerosol
concentrations typical of the coastal boundary layer suggests a I2 mixing ratio range of 6−93 pptv can account for the observed
particle production events. Aerosol number concentration produced from I2 is more than a factor of 10 higher than that
produced from CH2I2 for the same mixing ratios.