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The type of emissions matters – CO2 vs. SO2 and NO2

The type of emissions matters

Sometimes, you may come across the claim that a large container ship has emissions like millions of vehicles. But we must note that the type of emissions matters.

This statement is true, but not in the case of CO2 emissions. This statement may relate to emissions of sulfur dioxide (SO2) and nitrogen dioxide (NO2). CO2 emissions contribute to global warming, while SO2 and NO2 emissions cause local air pollution.

Regarding CO2 emissions, almost all these ships run on fossil fuels, emitting much carbon pollution. Maritime shipping, which transports about 90% of world trade, accounts for nearly 3% of the world’s CO2 emissions. Ships transport more than 10 billion metric tons of cargo each year. There are now over 100,000 transport ships at sea, of which about 6,000 are large container ships. Note that these ships are powered by very powerful engines, such as the 11-cylinder straight engine (Ever Given ship), which produces 59,300 kW (79,500 horsepower) at 79 rpm. Although ships are the most energy-efficient method in the movement of a given mass of cargo at a given distance, the sheer size of the maritime transport industry means that it significantly affects the environment. The increasing annual amount of shipping overwhelms gains in efficiency, such as from slow-steaming. Slow steaming is the practice of operating transoceanic cargo ships, especially container ships, at significantly less than their maximum speed.

Regarding sulfur dioxide (SO2) and nitrogen dioxide (NO2) emissions of total global air emissions, shipping accounts for 18 to 30 percent of the nitrogen oxide and 9% of the sulfur oxides. Air pollution from ships is generated by diesel engines that burn high sulfur content fuel oil, also known as bunker oil, producing sulfur dioxide, nitrogen oxide, and particulate, in addition to carbon monoxide and carbon dioxide.

Sulfur dioxide (SO2) and nitrogen dioxide (NO2) emissions are important air pollutants and are also recognized as the main pollutants of ship emissions. Both can engage in atmospheric chemical reactions to produce aerosols and acid rain, and further have negative effects on the air quality, climate system, human health, and acidification of terrestrial and marine ecosystems. It affects the air quality in coastal areas and even influences the inland areas hundreds of kilometers away from the emission sources. The port city is the most affected by ship pollution, followed by cities along the river.

To reduce the negative impacts of ship emissions, the European Union and the United States have implemented regulations in an effort to decrease ship emissions, among which the fuel quality regulation has been proven to be the most effective measure for addressing the issue of sulfur oxides (SOx) and particulate matter (PM) emissions in many countries.