A model study was performed to investigate the initial fate of nanometer-size nuclei formed in the atmosphere by homogeneous nucleation. Two important results were obtained: (1) coagulational scavenging into preexisting aerosol particles is an extremely strong sink for nuclei formed recently in the atmosphere, and (2) the growth of fresh nuclei to detectable sizes and above requires in most cases the presence of nonvolatile condensable vapors other than H2SO4(g). These vapors are probably secondary organics, and their total required concentration level ranges from <107 up to 108 molecules cm-3 depending on the preexisting particle population. The fact that newly formed particles are scavenged significantly or even totally before reaching detectable sizes has important consequences when interpreting atmospheric measurements. First, atmospheric nucleation events are probably much more frequent than what has been believed based on earlier observations, and second, the nucleation rates derived from atmospheric observations are likely to be substantially lower than the rates at which new particles are really formed by nucleation. Since newly formed nuclei will be scavenged away unless they grow sufficiently fast, there must be some lower limit for the nuclei growth rate below which the nucleation event will not be recorded using the current measurement techniques. The minimum growth rate was estimated to be below 1 nm h-1 in clean environments and of the order of several nm h-1 in polluted environments. This requirement may explain why observed atmospheric particle formation events are accompanied frequently by the growth of new particles to sizes typical of the Aitken mode. ¿ 2001 American Geophysical Union