Effervescent nozzle design to enable outdoor marine cloud brightening experimentation

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.