Stratospheric Single Particle Characterization with Particle Analysis by Laser Mass Spectrometry - Next Generation (PALMS-NG)

Stratospheric particles play a critical role in the heterogeneous chemistry of ozone depletion and climate change. Despite their importance, the chemical composition and origin of stratospheric particles remain poorly constrained. Uncertainties increase with atmospheric perturbations, such as strong convection and overshooting of the tropopause from intense summer storms, which may rapidly transport aerosols from the troposphere to the stratosphere. In order to characterize particles in the stratosphere, investigate their internal and external mixing states, and understand the impact of convection on the stratospheric composition, we deployed a newly developed airborne single particle mass spectrometer, Particle Analysis by Laser Mass Spectrometry - Next Generation (PALMS-NG), on the NASA's ER-2 aircraft which can reach up to ~21 km altitude, during the Dynamics and Chemistry Of The Summer Stratosphere (DCOTSS) research project in 2021 and 2022.

PALMS-NG has been developed with updated features compared to the original flight PALMS. Specifically, 1) particle detection is improved with a size range of ~100 nm to > 3 µm (formerly ~150 nm to ~3 µm) and higher detection efficiency (1-4 orders of magnitude improvement at sizes < 200 nm); 2) bipolar mass spectra with higher ion mass resolution (increased by a factor of 5) can be obtained by using a pair of s-shaped time-of-flight mass spectrometers (sTOFs). Utilizing the enhanced capabilities of the PALMS-NG and the large altitude range of the ER-2, we have identified various particle types, including pure sulfuric acid, meteoric, mercury and halogen-containing, perchlorate-containing, organosulfate-containing, ammonium sulfate, and biomass burning particles in the stratosphere, indicating natural and anthropogenic origins. Furthermore, we found that halogens can condense on most of the particle types but with different tendencies, suggesting certain particle types may preferentially promote chlorine activation/ozone depletion. Our results from the DCOTSS mission will provide a more complete view of stratospheric particles and advance our understanding of stratospheric aerosol chemistry.