New and upcoming emission control areas

Shipping has long been one of the most energy-efficient modes of global transportation. However, despite its efficiencies, the industry has contributed to air pollution. Ships can emit large quantities of sulphur oxides (SOₓ) from burning heavy fuel oil with high sulphur content, and nitrogen oxides (NOₓ) from high-temperature combustion processes in marine engines. 

The environmental impact of these emissions is potentially significant and, recognising these issues, the International Maritime Organization (IMO) established a global framework to regulate emissions from ships under the International Convention for the Prevention of Pollution from Ships (MARPOL). 

Milestones in Sulphur Emissions Regulation 

The cornerstone of the IMO’s efforts was the adoption of MARPOL Annex VI in 1997, which entered into force in 2005. This marked the first global treaty dedicated specifically to addressing air pollution from ships. It introduced a global sulphur cap of 4.5% by mass in marine fuels and, importantly, allowed for the establishment of Emission Control Areas (ECAs) where even stricter standards could be enforced. 

Over the years, these standards have become more stringent. In 2012, the global sulphur limit was lowered to 3.5%, marking an important step towards cleaner shipping. The most significant change occurred with the introduction of "IMO 2020," which, starting January 1, 2020, reduced the allowable global sulphur content in marine fuel to 0.50%. This regulation required ships to switch to very low sulphur fuel oil (VLSFO), marine gas oil (MGO), or install scrubbers to clean exhaust gases. 

In Emission Control Areas (ECAs), the regulations are even stricter. In existing ECAs such as the Baltic Sea, North Sea, North America, the United States Caribbean Sea, and the Mediterranean Sea (starting May 1, 2025), the maximum allowable sulphur content in marine fuels is limited to 0.10%. Ships operating in these zones must use compliant fuels like marine gas oil (MGO) or ultra-low sulphur fuel oil (ULSFO). Alternatively, they can install scrubbers to continue using higher-sulphur fuels. 

Milestones in NOₓ Emissions Regulation 

Alongside the efforts to reduce sulphur emissions, the IMO introduced a tiered approach to address nitrogen oxide (NOₓ) emissions from ship engines. The first level, Tier I, applied to ships built from 2000 onwards and required modest reductions in NOₓ emissions. For ships built from 2011, Tier II standards imposed stricter limits on newer vessels. 

A significant milestone was reached on January 1, 2016, when Tier III emission standards were enforced for ships constructed on or after this date and operating within existing NOₓ Emission Control Areas (ECAs). At that time, the North American coasts and the US Caribbean Sea were designated as NOₓ ECAs. Tier III standards demand up to an 80% reduction in NOₓ emissions compared to Tier I standards. This reduction is achievable through advanced technologies such as Selective Catalytic Reduction (SCR) systems or Exhaust Gas Recirculation (EGR) and also depended on the fuel type. 

In 2021, the Baltic Sea and North Sea also adopted Tier III standards, further tightening controls on NOₓ emissions in these busy maritime corridors. The Tier III standards apply to ships constructed after January 1, 2021 and visiting these areas. "Constructed" refers to ships whose keels are laid or which are at a similar stage of construction.  

The table below outlines the applicable NOx tiers for ships operating within existing Emission Control Areas (ECAs) and those operating outside these areas: