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Global models predict that new particle formation (NPF) is, in someenvironments, responsible for a substantial fraction of the totalatmospheric particle number concentration and subsequently contributessignificantly to cloud condensation nuclei (CCN) concentrations. NPF eventswere frequently observed at the highest atmospheric observatory in theworld, on Chacaltaya (5240 m a.s.l.), Bolivia. The present study focuses on theimpact of NPF on CCN population. Neutral cluster and Air Ion Spectrometerand mobility particle size spectrometer measurements were simultaneouslyused to follow the growth of particles from cluster sizes down to∼ 2 nm up to CCN threshold sizes set to 50, 80 and 100 nm.Using measurements performed between 1 January and 31 December 2012, wefound that 61 % of the 94 analysed events showed a clear particle growthand significant enhancement of the CCN-relevant particle numberconcentration. We evaluated the contribution of NPF, relative to thetransport and growth of pre-existing particles, to CCN size. The averagedproduction of 50 nm particles during those events was 5072, and1481 cm<sup>−3</sup> for 100 nm particles, with a larger contribution of NPFcompared to transport, especially during the wet season. The data set wasfurther segregated into boundary layer (BL) and free troposphere (FT)conditions at the site. The NPF frequency of occurrence was higher in the BL(48 %) compared to the FT (39 %). Particle condensational growth wasmore frequently observed for events initiated in the FT, but on averagefaster for those initiated in the BL, when the amount of condensable specieswas most probably larger. As a result, the potential to form new CCN washigher for events initiated in the BL (67 % against 53 % in the FT). Incontrast, higher CCN number concentration increases were found when the NPFprocess initially occurred in the FT, under less polluted conditions. Thiswork highlights the competition between particle growth and the removal offreshly nucleated particles by coagulation processes. The results supportmodel predictions which suggest that NPF is an effective source of CCN insome environments, and thus may influence regional climate through cloud-related radiative processes

CCN production by new particle formation in the free troposphere