Particle Size Distribution Measurements for Stratospheric Aerosols in the Range of 0.003 to ~4.0 μm during the SABRE Mission
MING LYU, Charles Brock, Adam Ahern, Samuel Taylor, Troy Thornberry, Ru-Shan Gao, Eric Hintsa, Colin Gurganus, Andrew Rollins, Eleanor Waxman, Fred Moore, Geoff Dutton, David Nance, Brad Hall, Kristen Zuraski,
CIRES/NOAA Chemical Sciences Laboratory Abstract Number: 684
Working Group: Aerosol Physics
AbstractThe stratospheric aerosol layer plays an essential role in the Earth's radiation budget. Accurate measurement of the concentration and size distributions of stratospheric aerosol particles is crucial in constraining stratospheric radiative effects and their impact on climate. In-situ observations of nucleation mode aerosol particles in the upper troposphere/lower stratosphere are rare, but are of particular importance in understanding the contribution of upwelling ultrafine particles formed near the tropical tropopause and their subsequent evolution in the stratospheric (Brewer-Dobson) circulation.
In the SABRE (Stratospheric Aerosol processes, Budget and Radiative Effects) mission from January to March 2023, we used the Aerosol Microphysical Properties (AMP) instrument suite on a high-altitude aircraft to measure the number concentration and size distribution of aerosol particles in the size range from 0.003 to ~4.0 μm in the lower stratosphere through mid- to high latitudes. Simultaneous trace gas measurements, including O
3, N
2O, SF
6, SO
2, and OCS, were used to investigate dynamical and chemical processes in the stratosphere that determine the evolution of aerosol microphysics. Preliminary results have shown a bimodal structure for stratospheric aerosols in the size distribution; the peak of the small mode is at diameters < 0.1 μm (the troposphere mode), which has not been measured in most previous missions, and the peak for the larger mode is > 0.2 μm diameter (the stratosphere mode). These two modes change as a function of the age of air in the stratosphere (as shown by O
3, N
2O and SF
6), and the evolution in the size of these two modes suggests condensational growth of the troposphere mode particles. These are the first observations of the presence and evolution of this bimodal aerosol structure deep into the stratosphere. The presence of a tropospheric mode of smaller particles in the stratosphere may have implications for proposed geoengineering approaches.