On the Fate of Aerosols Produced by New Particle Formation in the Upper Troposphere and Lower Stratosphere

New particle formation (NPF) in the upper troposphere and lower stratosphere (UTLS) has been suggested to contribute to cloud condensation nuclei in the troposphere, as well as for maintaining the stratospheric aerosol layer over the Asian summer monsoon (ASM). However, the fate of newly formed particles and their potential impact on climate are largely unknown. Here we use in situ aircraft measurements of aerosol size distributions collected in the UTLS over the eastern ASM region, combined with Lagrangian trajectory modeling and satellite‐derived convection, to show that NPF events primarily occur downstream of convection in the upper troposphere (below the tropopause) between 350 and 360 K potential temperature levels. While the majority of air parcels containing NPF events descend into the lower troposphere, approximately 20% of NPF event parcels ascend into the stratosphere and thereby may contribute as a source of material to the stratospheric aerosol layer. Plain Language Summary Certain gases in the atmosphere, under the right conditions, can condense to form stable particles. These newly formed particles in the atmosphere are very small upon formation, but can grow to larger sizes and play an important role in climate. For example, in the troposphere, these particles may serve as nuclei for cloud formation. In the stratosphere, they may contribute to the maintenance of an aerosol layer that influences Earth's radiation budget. Analyses of high‐altitude aircraft measurements over the Asian summer monsoon region reveal an abundance of new particles in the upper troposphere and downstream of convection. While the majority of air parcels that contain these newly formed particles descend to lower altitudes, we found that approximately 1/5 (20%) of them ascend into the stratosphere within a few months. We expect the ascending parcels, whether they still contain particles or as precursor gases, to contribute to the overall composition of the stratosphere.