The International Maritime Organization (IMO) is an intergovernmental organization

responsible for the safety of shipping and the prevention of marine pollution.

One of the IMO’s most important achievements is the implementation of MARPOL

(International Convention for the Prevention of Pollution from Ships) Annex 6,

which regulates air pollution from ships.

Objectives of MARPOL Annex 6

aerial view of a cargo ship emitting CO2

Photo credit

MARPOL Annex 6 aims to control and reduce air pollution from ships by setting strict limits on emissions of harmful substances. Its primary objectives are:

  • Reduce sulfur oxide (SOx) emissions: SOx emissions contribute to acid rain, smog, and other forms of air pollution. Annex 6 sets limits on the maximum allowable sulfur content in fuel oils used by ships, leading to a significant reduction in harmful SO2 emissions.
  • Control nitrogen oxide (NOx) emissions: NOx emissions contribute to smog, acid rain, and climate change. Annex 6 establishes tiered limits for NOx emissions based on engine type, ensuring ships meet stringent standards to minimize NOx pollution.
  • Address greenhouse gas (GHG) emissions: While Annex 6 does not directly target GHG emissions, it indirectly contributes to their reduction by promoting the use of cleaner fuels and more efficient technologies.

Key Provisions of MARPOL Annex 6

  • Sulfur limits: Annex 6 imposes global and regional sulfur limits, with the global limit currently set at 0.50% m/m (mass by mass) for most maritime areas. Emission Control Areas (ECAs) have even stricter limits, such as 0.10% m/m.
  • NOx emission standards: The regulation outlines tiered NOx emission limits based on engine power and age. It encourages the use of technologies like Selective Catalytic Reduction (SCR) and Exhaust Gas Recirculation (EGR) to achieve compliance.
  • Energy Efficiency Design Index (EEDI): Annex 6 introduces the EEDI, which sets minimum energy efficiency standards for new ships. It encourages the development and adoption of more fuel-efficient vessel designs.
  • Shipboard emission monitoring: The regulation requires ships to monitor and report their fuel consumption, operating hours, and relevant emission data. This promotes transparency and helps enforce compliance.
sulphur emission ship

sulphur emission ship

Impact on the Maritime Industry

MARPOL Annex 6 has had a profound impact on the maritime industry, driving significant changes and advancements. Here are some notable effects:

  • Shift towards low-sulfur fuels: Ship operators have transitioned from high-sulfur fuel oils to low-sulfur alternatives, such as marine gas oil (MGO) and liquefied natural gas (LNG), to meet the sulfur limits. This has led to reduced air pollution and improved air quality in coastal areas.
  • Technology advancements: Annex 6 has stimulated research and development in emissions control technologies, such as scrubbers, exhaust gas cleaning systems, and innovative engine designs. These advancements promote cleaner and more efficient maritime operations.
  • Market dynamics and cost implications: Compliance with Annex 6 has influenced fuel costs, supply chain logistics, and vessel competitiveness. Shipowners and operators have had to make strategic decisions regarding fuel selection, retrofitting, or new building options to maintain compliance while managing operational costs.


MARPOL Annex 6 stands as a vital instrument for curbing air pollution in the maritime industry. By setting emission standards and promoting sustainable practices, it contributes to a greener future for global shipping. Embracing its objectives and provisions fosters a cleaner environment, enhances maritime safety, and supports the industry’s sustainable development.