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 mu mol 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 (similar to 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 CH2I2 for the same mixing ratios.