Single Particle Properties of Aerosol from over the Southern Atlantic Ocean from the CLARIFY (2017) and ORACLES (2017 and 2018) Campaigns

Abstract:

Aerosol properties of mixing state, chemical composition, morphology and microstructure affect aerosol radiative properties and ability for the aerosol to act as a cloud condensation nuclei. Both NASA’s ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) and the UK’s CLARIFY (CLoud-Aerosol-Radiation Interactions and Forcing) studies seek to reduce uncertainty in aerosol-radiation and aerosol-cloud interaction in the southeast Atlantic, a region of high aerosol loading as well as a semi-permanent stratocumulus cloud deck. In-situ aerosol measurement methods allow for high temporal resolution but do not provide detailed single particle information that includes mixing state, morphology and elemental composition. Improved representation of these properties can reduce uncertainty on aerosol-radiation and aerosol-cloud effects in the southeast Atlantic, a region of importance due to its high aerosol optical depths and model uncertainties.

We present findings from transmission electron microscopy (TEM) coupled with energy dispersive X-ray (EDX) from 34 filters collected during the campaigns. The results of aerosol size, elemental composition, morphology and particle type highlight a dominance of potassium salts, a large marine influence, new particle formation over the ocean, and differences in volatility and viscosity of the organic between the two campaigns. As well, a range of mixing states from core shell, dimer and aggregate configurations have been found, with mixtures including organic and salts in varying consistencies and black carbon in a predominantly condensed configuration.