Aerosols in the upper troposphere and lower stratosphere (UTLS) are crucial to understanding radiative forcing, ice cloud formation, and ozone chemistry. In-situ aircraft measurements with fast chemical composition sensors are essential to further our understanding. Mass spectrometers such as Aerodyne Aerosol Mass Spectrometers (AMS) and Particle Analysis by Laser Mass Spectrometry (PALMS) have been used for these measurements. Such instruments typically use an aerodynamic lens as an inlet that collimates aerosols into a small detection volume over a wide range of particle sizes. However, such lenses depend on a constant upstream pressure to work consistently, and airborne interfaces that provide that (pressure-controlled inlets –PCI-) have historically performed poorly at high altitudes. In this study, we are developing and testing a new PCI coupled with a recently developed PM2.5 aerodynamic lens towards the goal of sampling PM1 aerosols up to ~16 km altitude. We use state-of-the-art fluid dynamic models to inform development and testing. We characterize the transmission efficiency (TE) as a function of particle size over the range of pressures relevant for airborne sampling. As part of this project, a new lens alignment tool and a new particle beam imaging device, based on the Aerodyne aerosol Beam Width Probe (BWP) have been developed and tested. We show the current performance of PCI and compare it with existing inlet systems.