Reducing Ship Air Pollution: Strategies For Cleaner Seas

Air pollution from ships is a pressing issue that has detrimental effects on both human health and the environment. The commercial marine shipping industry is a major contributor to global air pollution, and without intervention, the industry's emissions are expected to increase. To combat this, new regulations and practical initiatives are being implemented to reduce air pollution from ships.

One of the key approaches to reducing air pollution from ships is through the implementation of international conventions and regulations. The International Maritime Organization (IMO), for example, has introduced several measures to limit emissions. These include the International Convention for the Prevention of Pollution from Ships (MARPOL), which sets limits on sulphur oxide and nitrogen oxide emissions from ship exhausts and prohibits the deliberate emission of ozone-depleting substances.

In addition to regulatory measures, there are also technological advancements and operational efficiencies being explored to reduce air pollution from ships. This includes the use of alternative energy sources such as wind, solar power, batteries, biofuels, and hydrogen fuel cells. Moreover, modifications to ship components, such as engine improvements and the use of exhaust gas cleaning systems, are also being utilized to reduce emissions.

The efforts to reduce air pollution from ships are crucial to mitigating the negative impacts on human health and the environment, with poor air quality being linked to various health issues and contributing to climate change.

Reduce sulphur oxide emissions

Sulphur oxides (SOx) are harmful to human health, causing respiratory, cardiovascular, and lung disease. Once released into the atmosphere, SOx can lead to acid rain, which impacts crops, forests, and aquatic species and contributes to ocean acidification.

To reduce sulphur oxide emissions from ships, the International Maritime Organization (IMO) has implemented several measures as part of the International Convention for the Prevention of Pollution from Ships (MARPOL).

MARPOL Annex VI

The MARPOL Annex VI, first adopted in 1997, limits the main air pollutants contained in ships' exhaust gases, including sulphur oxides (SOx). Following revisions in 2008, the updated MARPOL Annex VI aims for a progressive reduction in SOx emissions globally and the introduction of specific emission control areas (ECAs) to further reduce air pollutants in designated sea areas.

Emission Control Areas (ECAs)

The ECAs established by the IMO include the Baltic Sea, the North Sea, the North American area (covering designated coastal areas of the US and Canada), and the US Caribbean Sea area. Within these ECAs, stricter limits on sulphur emissions are enforced, with a maximum sulphur content of 0.10% for fuel oil used in ships.

Global Sulphur Limit

In addition to the ECAs, the IMO has implemented a global sulphur limit for ships operating outside the designated ECAs. From January 1, 2020, the sulphur content in the fuel oil used onboard ships was limited to 0.50% m/m (mass by mass), a significant reduction from the previous limit of 3.5%.

Alternative Methods

Some ships install exhaust gas cleaning systems, also known as "scrubbers," to limit air pollutants. These systems remove sulphur oxides from the ship's engine and boiler exhaust gases, allowing the ship to use heavy fuel oil while still complying with the sulphur emission limits.

Alternative Fuels

Ships can also switch to alternative fuels with low or zero sulphur content, such as liquefied natural gas or biofuels. New blends of fuel oil, such as blending gas oil with heavy fuel oil, have been developed to meet the sulphur limits.

Compliance and Enforcement

Compliance with the sulphur emission limits falls under the responsibility of governments and national authorities of member states that are parties to MARPOL Annex VI. Flag states (the state of registry of a ship) and port states have rights and responsibilities to enforce compliance. The IMO has issued guidelines and standardized forms to support consistent implementation and facilitate reporting and verification processes.

Reduce nitrogen oxide emissions

Nitrogen oxides (NOx) are formed when fuels such as oil, gas, and coal are burned at very high temperatures. NOx emissions contribute to global warming and are extremely dangerous. They can cause lung inflammation and increase susceptibility to allergens in people with asthma. NOx emissions also interact with volatile organic compounds to create ground-level ozone, which can cause eye, nose, and throat irritation, shortness of breath, and respiratory issues.

To reduce NOx emissions from ships, the following methods can be implemented:

• Selective Catalytic Reduction (SCR) System: This is currently the most efficient method, reducing NOx emissions by 90-95%. It involves mixing a reagent (SCR 40 – 40% Marine Urea Solution) with the exhaust gas to convert nitrogen oxides into nitrogen (N2), water, and carbon dioxide (CO2).
• Exhaust Gas Recirculation (EGR): This technique recirculates the exhaust gas or introduces water into the engine to reduce NOx emissions.
• Fuel Switching: Switching from marine fuel oils to alternative fuels such as liquefied natural gas (LNG) or methanol can help reduce NOx emissions. LNG, for example, can reduce NOx emissions to Tier III levels.
• Reduced Fuel Consumption: Slowing down the speed of ships can help reduce fuel consumption and, consequently, lower NOx emissions. This method is known as slow steaming.
• Engine Modifications: Internal engine modifications, such as adding water, recirculating exhaust gas, cooling water temperatures, or adjusting the intake valve closing, can effectively reduce NOx emissions.
• Emission Control Areas (ECAs): Establishing designated areas with stricter NOx emission standards, such as the North American Emission Control Area, can significantly reduce NOx emissions from ships operating in those regions.
• Economic Instruments: Implementing economic measures such as levies or funds can provide incentives for ship operators to adopt NOx abatement measures, leading to reduced emissions.

Ban heavy fuel oil in the Arctic

Heavy fuel oil (HFO) is the bottom of the barrel in terms of oil refining. It is incredibly thick and sticky, and at room temperature, it can be as viscous as peanut butter. Because of its low quality, it is only really used in marine transport. HFO is the preferred fuel for the marine shipping industry because it is cheap, widely available, and large marine engines are built to handle it. However, it is incredibly dangerous to human and environmental health and is considered the most significant threat to the Arctic.

In the Arctic, HFO is commonly used by vessels engaged in community resupply, bulk carriers serving mining projects, and some larger fishing vessels. A spill in the Arctic would have grave consequences given the limited marine traffic and infrastructure in the region. HFO does not evaporate quickly, so it is more likely to be trapped in ice, making it very difficult to recover. It also does not readily disperse or break down in the marine environment and tends to stick to surfaces like sea ice or emulsify in seawater. The remote location of the Arctic and its extreme weather conditions would also make an HFO spill challenging, costly, and dangerous to clean up.

In recognition of the threat posed by HFO, the Government of Canada announced its support for a global ban on HFO in the Arctic in February 2020. This was followed by the International Maritime Organization (IMO), the governing body for international shipping, announcing a ban on the use and carriage of HFO in the Arctic, to come into force on July 1, 2024. This ban will be implemented through an Interim Order while the regulations are being amended. All double-hulled ships will be exempted from the ban until July 1, 2029, and ships involved in Arctic community resupply can apply for a waiver until July 1, 2026.

The ban on HFO in the Arctic is a crucial step towards protecting the fragile Arctic environment and the well-being of northern communities. It is also part of a broader effort to reduce the environmental impacts of marine shipping and grow a clean net-zero economy. By banning HFO, we can reduce the risk of disastrous oil spills and mitigate the effects of shipping emissions on surrounding communities and ecosystems. Additionally, this ban demonstrates a commitment to balancing environmental protection with the economic needs of northern Indigenous and Inuit communities who rely on HFO for resupply.

While some businesses have expressed concerns about the potential financial impact of the ban, it is important to prioritize the long-term sustainability of the Arctic region and explore alternative fuel sources. The transition to cleaner fuels may come with initial costs, but the benefits of reducing air pollution from ships and protecting the Arctic ecosystem outweigh the economic concerns.

Implement Emission Control Areas

Emission Control Areas (ECAs) are designated sea areas that enforce stricter controls to minimise airborne emissions from ships. Initially, the regulation was aimed at reducing sulphur oxide (SOx) emissions, but in 2005, it was extended to include nitrogen oxide (NOx) restrictions in several areas.

The International Maritime Organisation (IMO) has played a significant role in regulating ship pollution through the International Convention for the Prevention of Pollution from Ships, known as the MARPOL Convention. The "1997 Protocol" updated the MARPOL Convention to include Annex VI, which specifically addresses the prevention of air pollution from ships.

The implementation of ECAs is a crucial strategy to reduce air pollution from ships. These designated areas enforce stricter emission standards, particularly for SOx and NOx. As of 2015, ships operating in ECAs are required to use fuel with a maximum sulphur content of 0.1%, compared to the 0.5% limit outside these areas. This regulation has had a positive impact on air quality and human health, especially in coastal regions.

To comply with the ECA requirements, shipowners can choose between changing to low-sulphur fuels, such as Marine Gas Oil (MGO) or Marine Diesel Oil (MDO), or installing scrubbers to remove SOx from exhaust gases. For NOx reduction, options include Selective Catalytic Reduction (SCR), Exhaust Gas Recirculation (EGR), and the use of Liquified Natural Gas (LNG) in lean-burn engines or turbines.

The United States has established two ECAs: the North American ECA and the US Caribbean Sea ECA. Additionally, Canada's Atlantic and Pacific coastal waters below the 60th parallel are protected under the North American ECA. The establishment of these ECAs has led to significant reductions in emissions from ships, bringing about notable health and environmental benefits.

Improve engine and fuel efficiency

Improving engine and fuel efficiency is a crucial aspect of reducing air pollution from ships. Here are some detailed strategies and technologies to achieve this:

Transition to Lower-Sulfur Fuels:

• One of the most effective ways to improve fuel efficiency and reduce air pollution is by transitioning to low-sulfur fuels. This includes the use of low-sulfur marine fuels or alternative fuels such as marine diesel oil (MDO) and liquefied natural gas (LNG).
• For example, the Sulphur Content of Marine Fuels (SCMF) Directive in Europe has implemented sulfur limits for marine fuels used in specific regions and by passenger ships, contributing to a significant reduction in sulfur dioxide (SO2) emissions.

Exhaust Gas Cleaning Systems:

• Exhaust gas cleaning systems, also known as scrubbers, can be used to remove sulfur oxides (SOx) and particulate matter from ship emissions.
• These systems mix the exhaust with caustic soda or seawater, achieving removal rates of up to 99% for SOx and 98% for particulate matter.

Selective Catalytic Reduction (SCR):

• SCR technology treats exhaust gases before their release, significantly reducing nitrogen oxides (NOx) emissions.
• It involves injecting a reducing agent, such as ammonia or urea, into the exhaust stream, which reacts with NOx to form harmless nitrogen and water vapor.

Engine Modifications:

• Internal engine modifications can be made to reduce NOx emissions. This includes adding water, recirculating exhaust gas, cooling water temperatures, or adjusting overlap timing and intake valve closing.
• Gas-fuelled engines that use LNG or methanol can also be employed, reducing NOx emissions by up to 90% and SOx and particulate matter by 95-100% compared to heavy fuel oil (HFO).

Energy Efficiency Design Index:

• The International Maritime Organization (IMO) introduced the Energy Efficiency Design Index in 2011, providing minimum energy efficiency standards for new ships.
• This index takes into account the shape of the hull, propeller, and rudder, as optimizing these components can reduce fuel consumption by up to 15% for vessels over 5,000 gross tonnes.

Ship Energy Efficiency Management Plan:

• The IMO's Ship Energy Efficiency Management Plan is adopted for all ships to monitor Energy Efficiency Operational Indicators and assist ship operators in evaluating fleet carbon dioxide (CO2) emissions.
• This plan helps identify areas where improvements can be made to increase fuel efficiency and reduce air pollution.

By implementing these strategies and technologies, significant reductions in air pollution from ships can be achieved, contributing to improved air quality and human health, especially in coastal areas and port cities.

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