We are conducting long-term measurements at remote sites in Siberia and the Amazon Basin. At both sites, we find the classical type of nucleation events to be exceedingly rare, which calls in question the source of new particles in pristine regions. Observations during an aircraft campaign over the Amazon Basin showed extremely high aerosol concentrations in the upper troposphere consistently on all flights. The regions in the immediate outflow of deep convective clouds were depleted in aerosol particles, confirming the convective clouds as sinks of atmospheric aerosols. In contrast, dramatically enhanced small (<90 nm diameter) aerosol number concentrations were found in UT regions that had experienced outflow from deep convection. Our findings suggest that aerosol production takes place in the UT from volatile material brought up by deep convection, which is converted to condensable species in the UT. Subsequently, downward mixing of upper tropospheric aerosol are a source of particles to the BL. This may be an important source of aerosol particles in the pristine troposphere, where new particle formation is not commonly observed. This may have been the dominant process supplying aerosols in the pristine atmosphere, making clouds the dominant control of both removal and production of atmospheric particles.