Cloud adjustments due to aerosols are still the largest uncertainty on total anthropogenic radiative forcing in climate models. A large part of this uncertainty is related to the number and spatial distribution of cloud condensation nuclei (CCN) in the global atmosphere. Aerosols from new particle formation (NPF) can grow to become CCN in the atmosphere. We recently flew a substantial aerosol payload on the NASA Atmospheric Tomography Mission (ATom): four sets of research flights over the remote Pacific and Atlantic oceans. The flights were conducted once in each of the four seasons, with near pole-to-pole coverage, and constant profiling between 0.2 and 12 km altitude. We measured aerosol size distributions between 3 to 4000 nm diameter, single particle and bulk aerosol composition. We compare these measurements with output from four global models with online aerosol microphysics: GEOS-Chem-TOMAS, GEOS-Chem-APM, CAM5-APM and CESM-CARMA. We observe high number concentrations of particles forming in the tropical upper troposphere, and then growing on descent to sizes where they can act as CCN by the time they reach the lower troposphere. While all the models show NPF in the tropical upper troposphere, they underestimate the magnitude and do not reproduce the same growth to CCN-sizes. This phenomenon may cover ~40% of the earth's surface, therefore models are missing a potential large contributor to aerosol-cloud-radiation interactions.