Preventing Air Pollution: Strategies For Cleaner Shipping

Air pollution from ships is a pressing issue that contributes to air quality problems and affects both human health and the natural environment. To address this, various regulations and initiatives have been implemented, such as the MARPOL Annex VI, which limits emissions of sulphur oxides (SOx), nitrous oxides (NOx), and particulate matter. The use of alternative energy sources, modifications to ship components, and operational efficiencies are also being explored to reduce air pollution from marine shipping. While ships are the most energy-efficient way to transport large volumes of cargo, they burn hydrocarbon fuels, creating air pollution that degrades air quality and adversely affects human health. This paragraph introduces the topic of preventing air pollution from ships, highlighting the challenges, existing measures, and the ongoing efforts to mitigate the environmental and health impacts of ship emissions.

Reducing sulphur oxide emissions by burning low-sulphur fuel oil

Burning low-sulphur fuel oil is an effective way to reduce sulphur oxide emissions from ships. This method is outlined in the MARPOL treaty, specifically Annex VI, which addresses air pollution from ocean-going vessels. The treaty was developed by the International Maritime Organization (IMO), a United Nations agency focused on maritime safety, security, and pollution prevention.

Annex VI of the MARPOL treaty includes requirements for both the manufacture and operation of vessels and engines, as well as fuel quality standards. These standards apply to ships operating in U.S. waters and within 200 nautical miles of the North American coast, known as the North American Emission Control Area (ECA).

To comply with the treaty, ships can switch to using very low sulphur fuel oil (VLSFO) or marine gas oil (MGO). These fuels have a lower sulphur content, reducing the amount of sulphur oxide released into the atmosphere when burned. The new "IMO 2020" regulation, which came into effect on January 1, 2020, reduced the upper limit of sulphur content in fuel oil for ships outside designated ECAs from 3.5% to 0.5%.

This reduction in the sulphur limit has had a significant impact, leading to a 70%-77% decrease in overall sulphur oxide emissions from ships. The health and environmental benefits of this reduction are substantial, particularly for populations living near ports and coasts. Sulphur oxides are linked to respiratory, cardiovascular, and lung diseases, and they contribute to acid rain, which harms crops, forests, and aquatic life.

In addition to burning low-sulphur fuel oil, ships can also install exhaust gas cleaning systems, known as "scrubbers," to remove sulphur oxides from engine and boiler exhaust gases. This method is accepted by the MARPOL Convention as an alternative way to meet the sulphur limit requirement.

Using scrubbers to clean the exhaust from marine engines

Exhaust gas cleaning systems, or scrubbers, are a technology designed to remove sulphur oxides from a ship's engine exhaust. They are an approved and regulated solution for ships to meet the sulphur content requirements, which limit the sulphur content in marine fuel to no more than 0.5%.

Scrubbers use either fresh or seawater to ''wash' engine exhaust gas, removing sulphur oxides from the exhaust. This method is called wet scrubbing, and it also picks up other potentially polluting substances in the exhaust gas, such as heavy metals and polycyclic aromatic hydrocarbons (PAHs). However, this means that the washwater will be discharged into the marine environment, potentially reducing water quality. To mitigate this, the IMO has established guidelines that specify requirements for the discharge of scrubber washwater. MARPOL regulations also require that the wash water is monitored before being discharged to ensure that its pH value is not too low.

Dry scrubbers are another type of scrubber that employs solid lime as the alkaline scrubbing material to remove sulphur dioxide from exhaust gases.

The use of scrubbers is controversial. While they are effective at removing sulphur oxides from ship emissions, they have been accused of threatening marine life, contributing to ocean acidification, and being complicit in the shipping industry's environmental impact.

Reducing nitrogen oxide emissions from marine diesel engines

Nitrogen oxides (NOx) are air pollutants that harm the environment and human health. NOx damages the lungs and has been linked to heart disease, lower birth weight in newborns, and an increased risk of premature death. NOx emissions also contribute to acid rain, which damages crops, vegetation, and infrastructure, and causes poor air quality in the form of smog.

To reduce NOx emissions from marine diesel engines, several regulations and technologies have been implemented:

• Global Regulations: The International Maritime Organization's (IMO) International Convention for the Prevention of Pollution from Ships (MARPOL) Annex VI sets tiered limits (Tiers I, II, and III) to reduce NOx emissions from marine diesel engines with a power output above 130 kW. These standards apply to both main propulsion and auxiliary engines, and vessels operating in or within 200 nautical miles of the North American Emission Control Area (ECA).
• National and Regional Regulations: Individual countries and regions have also implemented regulations to reduce NOx emissions. For example, the United States has enforced marine emission standards and released a penalty policy for violations of sulfur fuel standards. Australia has similar standards, with Tier I applying to pre-2011 installations and Tier II for new installations or major conversions since 2011.
• Engine International Air Pollution Prevention (EIAPP) Certificates: When purchasing new marine diesel engines, shipowners must ensure the engine has an EIAPP certificate and technical file, providing evidence of compliance with NOx emission standards. From 2023, engine suppliers will be required to issue these certificates at the point of sale in Australia.
• Alternative Fuels: Using alternative fuels or non-diesel engines may permit compliance with emission standards, although this approach may have economic and safety penalties.
• Selective Non-Catalytic Reduction (SNCR): This technology injects urea or ammonia into ducting at temperatures of about 1000°C, reducing NOx gases to nitrogen without a catalyst.
• Exhaust Gas Scrubbing: On an industrial scale, exhaust gases can be scrubbed with chemicals such as sodium hydroxide or hydrogen peroxide, which react with and remove NOx gases.

Regulating ozone-depleting substances and volatile organic compounds

The International Convention for the Prevention of Pollution from Ships, or MARPOL, is a treaty that addresses marine pollution from ships. MARPOL Annex VI, which came into force on 19 May 2005, specifically deals with air pollution from ocean-going ships. It establishes limits on nitrogen oxide (NOx) emissions and requires the use of low-sulphur fuel, reducing ozone-producing pollution.

Regulating ozone-depleting substances (ODS) and volatile organic compounds (VOCs) is a key part of MARPOL Annex VI. It prohibits the deliberate emission of ODS and regulates VOC emissions from tankers. The Montreal Protocol has set a phase-out timetable for major ODS, including chlorofluorocarbons (CFCs), halons, and hydrochlorofluorocarbons (HCFCs). The use of halons in ships was banned in two phases, with the first category of compounds banned in ships constructed from 19 May 1995 and the second category in ships constructed from 1 January 2020. MARPOL Annex VI also bans the installation of equipment containing ODS, including HCFCs, in ships constructed from 1 January 2020.

Port State Control (PSC) authorities may conduct detailed inspections of ships with onboard installations of systems and equipment containing HCFCs. Ship owners and operators are advised to evaluate these systems and make conscious decisions about modifying them using non-ODS substances. Any redundant equipment or material containing HCFCs should be landed ashore for appropriate decommissioning or disposal.

The United States Environmental Protection Agency (EPA) has implemented programs to protect the ozone layer under Title VI of the Clean Air Act. These include the ODS Phaseout Program, which aims to phase out the production and consumption of ODS, and the Significant New Alternatives Policy (SNAP) Program, which reviews and lists substitutes for ODS.

Implementing alternative energy sources and modifying ship components

The commercial marine shipping industry is a major contributor to global air pollution, and without intervention, the emissions are expected to increase. To prevent air pollution from ships, implementing alternative energy sources and modifying ship components are crucial strategies.

Alternative Energy Sources

One alternative energy source that can be utilised is shore-side electricity, which can power ships while they are docked at ports, reducing ship-sourced SOx, NOx, PM, and CO2 emissions. This method has been successfully implemented in some ports, and its wider adoption is encouraged.

Another alternative is the use of low-sulphur fuels, which can significantly improve air quality by reducing the sulphur content in shipping fuels. Low-sulphur fuels also offer operational benefits, such as smoother engine performance and reduced maintenance costs.

The development and utilisation of alternative fuels, such as hydrogen and ammonia, are also promising avenues. These fuels have the potential to reduce emissions and are already recognised by the IMO and the EU as viable alternatives.

Additionally, exploring renewable energy sources like wind propulsion, battery-electric propulsion, and biofuels can contribute to emission savings. These options provide a cleaner and more sustainable approach to powering ships.

Modifying Ship Components

Modifying ship components can also play a significant role in reducing air pollution. Optimising the hull shape and vessel superstructure can enhance energy efficiency and reduce fuel consumption by up to 15% for vessels over 5,000 gross tonnes. This modification can be applied to existing ships through retrofits, although the implementation may be limited by cost and time constraints.

Another modification includes installing closed-loop 'scrubbers' or exhaust gas cleaning devices to reduce SOx emissions. While open-loop scrubbers are associated with environmental concerns due to wash-water discharges, closed-loop scrubbers offer a more sustainable solution.

Furthermore, selective catalytic reduction (SCR) systems are effective in treating exhaust gases and reducing NOx emissions beyond Tier III standards. This technology is already in use by many ships and is particularly effective when combined with low-sulphur fuels.

In summary, implementing alternative energy sources and modifying ship components are essential strategies to prevent air pollution from ships. By adopting these measures, the shipping industry can significantly reduce its environmental footprint and contribute to improved air quality and public health.

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