Coral reef exposure increases aerosol and cloud condensation nuclei over the Great Barrier Reef

The Great Barrier Reef (GBR) is the largest reef ecosystem in the world and is home to diverse marine life. In situ measurements characterizing lower troposphere aerosol concentrations and dynamics over the GBR are lacking in the literature. In this study, we present analysis of multi-year in situ aerosol measurements over the GBR, showing, for the first time, direct observations of coral reefs contributing to aerosol loading over the reef. Our results show that aerosol concentrations over the GBR are typical of a clean coastal environment, and the aerosol loading over the GBR is primarily influenced by the long-range transport of aerosol particles. However, a non-negligible effect from local sources is also observed. The fraction of small aerosol particles in the particle population increases in air masses that pass over the coral reef ecosystem. Finally, our statistical modelling shows that cloud condensation nuclei concentrations over the GBR are dominantly driven by the availability of accumulation and Aitken-mode aerosol particles with negligible effects from local meteorology. While accumulation-mode particle concentrations have the strongest impact on cloud condensation nuclei concentrations, counterfactual modelling simulation shows that Aitken-mode concentrations can contribute up to 6 % to cloud condensation nuclei concentrations over the reef.