New high-altitude measurements have revealed a hidden population of extremely small, organic-rich aerosol particles in the lower stratosphere. The findings suggest that these ultrafine aerosols, likely lofted from the underlying troposhpere, are far more abundant and chemically influential than previously understood. The stratospheric aerosol layer, extending from roughly 8 to 35 kilometers above Earth's surface, plays a crucial role in regulating climate by reflecting sunlight and enabling chemical reactions that influence atmospheric composition. Yet, despite its importance, our understanding of its constituent particles remains incomplete, largely because existing instruments struggle to detect the smallest particles, which fall below their sensitivity thresholds. It's thought that extremely small particles from the lower atmosphere are transported into the stratosphere through processes such as tropical uplift, atmospheric mixing, intense storm systems, wildfire-driven convection, and even aircraft emissions. However, detailed information about their size distribution, which is critical for determining their volume, surface area, and role in chemical processes, has remained scarce.
Using data collected by a high-altitude research aircraft during the NASA Stratospheric Aerosol Processes, Budget, and Radiative Effects (SABRE) project in 2023, Ming Lyu and colleagues report detailed measurements of stratospheric particles ranging from 0.003 to 2.4 microns, capturing both their distribution and chemical compositions in regions up to 19 kilometers above Earth. In their analysis, Lyu et al. reveal notably high concentrations of extremely small, organic-rich aerosol particles, particularly in atmospheric regions influenced by recently transported air and within the polar vortex. Despite being exceptionally small, these particles dominate the surface area available for heterogeneous atmospheric chemistry and act as a significant condensation sink. Lyu et al. confirmed that many of these fine organic-rich particles originate from the lower atmosphere and subsequently interact with larger sulfur-based aerosols, including those formed from volcanic emissions. This interaction produces a complex, bimodal particle size distribution that current climate models fail to accurately reproduce.
