Effervescent nozzle design to enable outdoor marine cloud brightening experimentation

[Geoengineering News]

https://pubs.rsc.org/en/content/articlelanding/2025/ea/d5ea00073d

Authors: Luke P. Harrison, Chris Medcraft, and Daniel P. Harrison 

26 August 2025

Abstract

Marine Cloud Brightening (MCB) is a proposed solar radiation management technique whereby the albedo of low-lying clouds is artificially enhanced by the addition of Cloud Condensation Nuclei (CCN). It is generally accepted that these would be produced by atomisation of seawater to produce droplets which form appropriately sized artificial sea spray aerosol (SSA). Despite extensive theoretical consideration of the MCB concept, progress in understanding how perturbations to complex cloud microphysical processes would evolve has been hampered by the technical inability to produce the very large numbers of SSA required. To facilitate the first phase of outdoor experimentation a single MCB station should be capable of producing around 1015 per s CCN. Effervescent nozzle technology has been posited as potentially capable of meeting these requirements. Here we describe an effervescent nozzle design that produces ∼1.73 × 1012 per s SSA, with ∼71% of aerosols within a 30 to 1000 nm range (considered likely CCN), using ∼512 W of energy per nozzle. Producing 1015 CCN using this design would then require 814 nozzles and around 417 kW of energy, a demand that can be practically met on a research vessel. The nozzle described here is therefore sufficiently practical to facilitate outdoor in situ experimentation of MCB, enabling a new generation of perturbation experiments that directly probe cloud microphysical and radiative responses to aerosol.

Environmental significance

Marine cloud brightening is a solar radiation management technique that is being considered for the protection of ecosystems, through either global or regional application, including over the Great Barrier Reef. Despite over 30 years of theoretical research, outdoor field experimentation could not proceed until technology was developed which could produce the required quadrillions per second of nano-sized sea salt crystals from seawater. In this submission we describe the development and laboratory characterisation of the dual fluid effervescent seawater atomising nozzle which was the technological development that has enabled the world's first outdoor field trials of MCB to be undertaken within the Great Barrier Reef.

Source: Royal Society of Chemistry