In a global effort to reduce air pollution emanating from ships the international community will impose a significantly lower limit on the sulphur content of fuel oil for ships from 1 January 2020. Exhaust gas cleaning systems, hereinafter ‘scrubbers’, are generally-accepted in international law as an equivalent method of reducing emissions but are plagued by uncertainties concerning the environmental impacts of their washwater discharges on the marine environment. As of 1 January 2020, Singapore unilaterally prohibits ships in the port of Singapore from discharging washwater from open-loop scrubbers. This report introduces the international rules and standards on sulphur oxide emissions from ships before discussing this Singaporean practice. The international legal context of Singapore’s discharge prohibition is found in the concept of port state jurisdiction and comparable unilateral prohibitions by other port states. This report concludes with a comment on the contributions of unilateral measures to the multilateral framework on emissions from ships

Dr Arron N. Honniball, LL.M. is a distinguished scholar in Public International Law, particularly focusing on the Law of the Sea, state jurisdiction, and maritime governance.

📌 Current Role

• Senior Research Fellow, Max Planck Foundation for International Peace and the Rule of Law (since May 2021) (mpfpr.de)

🎓 Education & Academic Journey

• Ph.D. in Public International Law, Utrecht University (2019) – Dissertation: Extraterritorial Port State Measures… combat illegal, unreported and unregulated fishing (mpfpr.de)

• LL.M. (cum laude) in Public International Law, Utrecht University (2013) (mpfpr.de)

• Bachelor of Laws, University College London (First Class Honours, 2011) (mpfpr.de)

🛳️ Previous Experience

• Research Fellow, Centre for International Law (CIL), National University of Singapore (Apr 2019–Apr 2021) (mpfpr.de)

• Ph.D. Candidate at Netherlands Institute for the Law of the Sea, Utrecht (2014–2017) (mpfpr.de)

• Rhodes Oceans Scholar, Rhodes Academy of Oceans Law and Policy, Greece (May 2014) (mpfpr.de)

🧭 Research Interests & Projects

• Shipping & maritime jurisdiction (port‑state, flag‑state)

• Illegal, Unreported & Unregulated (IUU) fishing

• Maritime terrorism & delimitation in the ASEAN/Indian Ocean regions

• Polar law and international ocean governance (mpfpr.de, Cogitatio Press)

He has contributed to initiatives such as the ASEAN and IORA regional projects (mpfpr.de).

📚 Selected Publications

• The MARPOL Port State Jurisdiction Regime (2025)

• The Rise of Port State Control Detention Review Panels… (2025)

• “Nationals” at Forty: … Combat IUU Fishing (2023) (mpfpr.de)

• One Treaty to Apply Them All? Defining Maritime Terrorism… (2023) (Digital Commons)

📬 Contact & Language

• Email: honniball@mpfpr.de (via Max Planck Foundation) (mpfpr.de)

• Phone: +49 6221 91404 69 (mpfpr.de)

• Primary working language: English

Dr Honniball is widely recognized as an expert in ocean law, maritime jurisdiction, and international environmental governance. Let me know if you'd like summaries of his papers or deeper details on any of his work!