| 24 Jul 2026
Tracing vessel-generated sea spray aerosols to support marine cloud brightening
Abstract. The aim of Marine Cloud Brightening (MCB) is to purposely inject artificially generated sea spray aerosols (SSAa) into low-level marine clouds, increasing their albedo with the objective of cooling the ocean surface beneath the clouds. Over the Great Barrier Reef (GBR), Australia, MCB is under research as a potential intervention to alleviate coral bleaching. Attributing cloud microphysical perturbations to MCB requires the ability to detect and trace SSAa and distinguish that from other local sources, including the exhaust from research aircraft, research vessel, and generators used to power the MCB technology. Here, we present a novel “tracer” method using in situ airborne measurements of the non-volatile aerosol ratio to identify the aerosol plume emanating from the spraying vessel and apportion aerosols between SSAa and combustion exhaust. A total of 14 flights were analysed using downwind, upwind, crosswind, or a combination of these sampling legs. Aircraft-sampled plumes of SSAa and exhaust exhibited contrasting non-volatile properties. Aerosol plume detections were identified using aerosol number concentration, and a mixing ratio model was constructed to apportion the detected plumes between SSAa and exhaust particulates. The “tracer” method reliably allowed tracking of the vessel-generated SSAa across all sampling events as the plume spread downwind from the spraying vessel. The majority of sampled plumes were found to be mixed SSAa and exhaust. This technique enables the tracking and identification of MCB aerosol in the natural marine atmosphere without the addition of a chemical tracer. Reliable plume identification is a prerequisite for studying the transport and dispersion of MCB aerosols and determining how they influence aerosols and clouds in the marine boundary layer.
In this article, the authors present a method to distinguish sea spray aerosols, artificially generated by a spraying vessel, from other types of aerosols (exhaust or natural), based on measurements from an airborne probe flying above the vessel in various atmospheric conditions during a field campaign. They find that tracking the non-volatile to volatile fraction of aerosols provides a good indication of whether aerosols were generated artificially.
It was a pleasure to review this article. The writing is extremely clear and economical, describing the scientific objectives, methodologies and results with accuracy and detail. The article is short and to the point, but I have never found myself puzzled by missing information. The figures are well-designed, innovative, readable, easy to understand, and information-rich. Everything is appropriately labeled and cited. The bibliography is exhaustive and well-chosen. The discussion section brings up interesting points. Congratulations to the authors for producing this very nice piece of work.
As far as I'm concerned, I would see no problem if this article were published as-is. My only suggestion for improvement would be to include a few words about how artificial sea spray aerosols are generated. I don't think this is explained in the article.
Technical comments