Observation-based Constraints on the Condensational Growth of Marine Aerosol Particles to Cloud Condensation Nuclei in the Eastern North Atlantic

Abstract

The formation, persistence, and radiative properties of low-level marine clouds are exquisitely sensitive to the concentration of cloud condensation nuclei. Cloud condensation nuclei present in marine environments can be attributed to the long-range transport of biogenic and anthropogenic terrestrial particles, primary sea-spray aerosol formed through wave-breaking at the ocean surface, and nucleation and condensational growth of existing particles to cloud condensation nuclei active sizes by reactive trace gases emitted from the ocean. Accurate attribution of marine cloud condensation nuclei to each of these sources is necessary to evaluate the sensitivity of Earth’s radiation budget to key aerosol processes in marine environments. Despite the importance of marine gases, cloud condensation nuclei, and the chemistry connecting them, there are few simultaneous measurements of marine reactive trace gases, their oxidation products in the gas and particle phase, and particle distributions in the remote marine boundary layer that can be used as observation-based constraints for process models. This work focuses on the acquisition and analysis of these key measurements from the existing Eastern North Atlantic sampling site on Graciosa Island, in the Azores.

The overarching objective of this project is to determine the source of condensable material that contributes to the growth of Aitken-mode aerosol particles to cloud condensation nuclei in the remote marine boundary layer over the Eastern North Atlantic. This project has three specific objectives: 1) Determine the atmospheric abundance and distribution of key marine reactive gases and their oxidation intermediates at the Eastern North Atlantic site. These measurements will be used to examine how the distribution of the oxidation products of dimethyl sulfide and volatile organic compounds, in a composition and volatility framework, vary as air is sourced from different sectors. 2) Characterize particle number-size distributions and the chemical composition of particles growing to cloud condensation nuclei sizes and determine particle growth rates in the context of measurements of condensable material. These observations will be used to explore how particle composition responds to the abundance and speciation of marine reactive gases and the volatility distribution of oxidized organics. 3) Connect measurements of cloud condensation nuclei chemical composition and precursor gas concentrations with determinations of the composition of condensable mass inferred from hygroscopicity measurements.

To address these objectives, we will deploy a pair of high-resolution time-of-flight mass spectrometers for measurement of gas and particle chemical composition to the Eastern North Atlantic sampling site field station on Graciosa Island, in the Azores during Spring-Summer 2022. Successful completion of the proposed work will provide needed insight on the chemical drivers for particle growth over marine environments that can be directly compared with existing laboratory and model representations of marine boundary layer chemistry.