Measurements are presented of ambient nanoparticle distributions (2.7 to 10 nm diameter) in regions of high biogenic emissions encountered during the First Aerosol Characterization Experiment (ACE 1), November 15 to December 14, 1995. Large numbers of newly formed nanoparticles were observed directly downwind of penguin colonies on Macquarie Island (54.5 ¿S, 159.0 ¿W). In these regions, nanoparticle concentrations were also correlated with sulfuric acid (H2SO4(g)) gas concentrations. The measurements show that biogenic species, possibly ammonia (NH3), either by itself or with H2SO4, nucleated to form new particles at rates much higher than bimolecular H2SO4/H2O nucleation. Nanoparticle distributions evolved as air was advected away from the island showing clear evidence of growth of the newly formed particles. Observed growth rates were in the range of 2 to 5 nm h-1 and were about a factor of 4 to 17 times higher than the growth by condensing H2SO4(g) and associated water. The cause for fast growth of the newly formed particles is unknown. ¿ 1998 American Geophysical Union