As part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA)-Cooperative LBA Airborne Regional Experiment, airborne measurements of aerosol properties over the northeast Amazonian rain forest at an altitude range between 0.2 and 12.6 km were performed in March 1998. The particle number densities in the free troposphere, normalized to standard temperature and pressure, exceed number densities observed in boundary layer by a factor of 2--15. Typical number densities in the boundary layer were around 500 cm-3. The large difference in particle number density between the boundary layer and the free troposphere agrees with previous observations of the in situ new particle production in the free troposphere. Analysis of the air mass history showed that even after more than a week of transport in the middle free troposphere, the newly formed ultrafine particles were more than one third of the total aerosol number concentration. Aerosol size distributions between 0.006 and 3 ¿m, divided into six vertical layers, show a C-shaped vertical structure with high concentrations of accumulation mode aerosols in the mixing layer and in the free troposphere above 10 km. The lower concentrations were observed in the free troposphere between 4 and 8 km. Enrichment in accumulation mode aerosol at altitudes above 10 km was attributed to outflow from deep convective clouds.