the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Aug 2026
Airborne and marine microplastics in the Northern Indian Ocean: decoupled pathways traced by black carbon
Abstract. Microplastics (MPs) are increasingly detected in marine and atmospheric particulate matter, but their sources, transport, and air–sea exchange remain poorly constrained in remote marine regions. We investigated airborne microplastics (AMPs) and marine microplastics (MMPs) during a 1-month campaign at the Maldives Climate Observatory Hanimaadhoo and in adjacent coastal waters. Airborne particles were collected with a deposition box, and seawater was sampled at coastal sites. Particle morphology, size, and polymer composition were determined by optical microscopy and µ-Raman spectroscopy and evaluated alongside aerosol scattering and equivalent black carbon (eBC). AMP concentrations ranged from 0 to 10.3 MP m-3 (mean: 3.1 ± 2.8 MP m-3). MMP concentrations ranged from 120 to 2656 MP m-3 (mean: 876 ± 804 MP m-3), exceeding typical open-ocean values and indicating substantial local influence from inhabited islands and maritime activity. Significant differences in size distributions and pronounced compositional differences of AMPs and MMPs suggest weak coupling between the atmospheric and marine reservoirs. Low dry-season wind speeds probably suppressed wave breaking, bubble bursting, and sea-spray-mediated transfer from ocean to atmosphere. Instead, AMP variability coincided with polluted air-mass advection, elevated eBC, and enhanced aerosol scattering, indicating stronger control by regional atmospheric transport than by local marine emissions. These results show that remote island atmospheres are exposed to anthropogenic plastic aerosol transport and demonstrate the value of combining MP observations with established aerosol tracers to resolve plastic-particle pathways in marine environments.
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Status: open (until 15 Oct 2026)
- RC1: 'Comment on egusphere-2026-4321', Anonymous Referee #1, 30 Sep 2026 reply
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The manuscript is well written and presents important data on microplastic pollution connecting measurements between marine and air environments. I hope to see the manuscript accepted after one very minor revision:
Comment on line 42: "MPs are generally defined as plastic particles smaller than 5 mm and typically larger than 100 nm (Kum et al., 2025)." I checked the paper on Kum et al. and rather than giving a definition for a microplastic I understood that their conclusion is that there is no consensus for the definition for microplastic. Therefore in my opinion the paper is incorrectly cited. In fact Kum et al. write: "We have also observed that there has been a multitude of opinions and recommendations regarding the definition of microplastics."
My suggestion to you is to leave out the lower limit, and simply write: "MPs are typically defined as plastic particles smaller than 5 mm." If you want to give a specific definition, then cite carefully the original source, however, in your case, I don't think you need to give the exact definition as it varies.
Then I have one optional revision:
I would really like to see some Raman spectra added to the manuscript. In the appendix you show representative microscope images. If you could add some representative Raman spectra, that would really be a valuable addition for scientist using Raman. Adding the spectra into the appendix would be enough. But as said, this is optional.