MultiMINI8: A Multi-Stage Micro Inertial Impactor (MINI) for High-Altitude Aerosol Sampling

Understanding the sources, composition, and the impact of atmospheric aerosols is essential for enhancing our knowledge of air quality, cloud formation, and climate dynamics. Refractory aerosols, in particular, play a significant role in the Upper Troposphere and Lower Stratosphere (UTLS), where they influence radiation balance and cloud nucleation processes. However, the unique challenges of aerosol sampling in these high-altitude regions urges the development of specialized instruments.

In this study, we introduce the MultiMINI8 (Miniature Inertial Impactor 8-fold), an advanced aerosol sampling instrument specifically designed for high-altitude applications in the UTLS. It builds on the earlier MultiMINI (Kandler et al. 2007) model, which was based on the historical evolution of impactor technology for ground-based applications. The MultiMINI8 is optimized for aircraft-based sampling in the UTLS, incorporating lightweight materials, a refined aerodynamic design, and real-time data acquisition capabilities to enable high-resolution offline microscopic analysis. This instrument features a two-stage cascade impactor that collects up to eight aerosol samples per flight, with nominal cut-offs at 1 µm and 0.2 µm. This design allows for precise capture of particles ranging from 20 nanometers to several micrometers, focusing on low-concentration aerosols, such as refractory particles, which are critical for studying cloud formation and climate dynamics.

To avoid contamination and artifacts from lower altitudes during aircraft sampling, all lines are purged before sampling, and sample substrate swapping occur in low-contamination environments. This rigorous protocol ensures the collection of representative samples from the UTLS, free from unwanted aerosol carryover from lower atmospheric layers.

The MultiMINI8 instrument was tested during the TPEx campaign in early summer 2024 over northern Germany as part of the TPChange project(https://tpchange.de/). By its deployment in the real flight conditions, we expect to greatly improve our understanding and achieve a much clearer picture of aerosol distribution and composition within the UTLS.