New insights into superheated atomisation offer potential improvement in submicron particle size distribution for marine cloud brightening

[Geoengineering News]

https://www.sciencedirect.com/science/article/pii/S0169809526003741?via%3Dihub

Authors: Edmund Reardon, Adam Boies, Jake Chapman, Daniel Harrison, Dante McGrath, Hugh Hunt, Shaun Fitzgerald

25 May 2026

10.1016/j.atmosres.2026.109110

Highlights

•Majority (99.5%) of droplets from superheated atomisation of seawater are submicron.

•Potential improvement in marine cloud brightening sprayers with superheated spray.

•Effects of temperature and pressure on submicron particle size distributions.

•Increasing temperature narrows submicron particle size distributions.

•Reducing pressure or flow rate increases volume fraction of submicron particles.

Abstract

Marine cloud brightening (MCB) is a proposed regional or global cooling technique that aims to increase cloud albedo by increasing the number of cloud condensation nuclei in low-lying marine clouds. Spraying micron or submicron droplets of seawater at a sufficient rate is considered the most suitable method for generating salt crystals for this purpose.

The technique of effervescent spraying has been used in outdoor MCB field trials. This study explores superheated atomisation as an alternative technology.

The performance of a continuous steady-state superheated saline solution sprayer has been characterised across a wide range of operating parameters and the effects of temperature, pressure, and nozzle expansion chamber length on production rate and generated particle sizes have been quantified. Results show that the technology can achieve a monomodal aerosol size distribution of dry salt particles with a mode of 65-75 nm and a geometric standard deviation of 1.85 when using a converging nozzle with a 200 μm diameter orifice. By number, 99.5% of droplets generated are submicron and 87% are within a size range suitable for MCB. The superheated atomiser developed and tested in this study is found to have comparable energy requirements to effervescent technology but with narrower size distributions, a likely benefit for MCB. However, at optimum sprayer performance the measured production of submicron dry crystals accounted for 14% of the saline solution mass flow, approximately 3.2 times less than for effervescent spray. This indicates that 86% of the mass was contained in larger particles.

This study demonstrates that superheated atomisation could be a viable method for generation of salt aerosol for MCB, depending on the negative effects of the large particles or the ability to remove them through further system optimisation.

Source: ScienceDirect