We present the first direct measurements of coastal ozone deposition and ultrafine particle emission fluxes alongside observation of particle growth to sizes where they will be active as cloud condensation nuclei (CCN). Simultaneous ozone deposition and particle emission from exposed macroalgae were observed during daytime low tide. Ozone deposition to seawater at high tide was significantly slower (vd[O3] = 0.302 ± 0.095 mm s−1) than low tidal deposition. Low tide deposition was slower at night (1.00 ± 0.10 mm s−1) than during daytime (2.05 ± 0.16 mm s−1) when ultrafine particle formation results in apparent particle emission. Particle emission fluxes greater than 200,000 cm−2 s−1 were observed during some of the lowest daytime tides and these particles grew large enough to act as CCN. These results provide the first direct evidence of both direct depositional loss and photochemical destruction of ozone in the formation of particles from macroalgal emissions at a coastal location.