Scrubbers, or exhaust gas cleaning systems, are installed on ships to reduce air pollution caused by sulfur oxides (SOx) emitted when burning heavy fuel oil. [1] A prevalent type is the open loop scrubber, which uses seawater to wash exhaust gases and then discharges the resulting polluted washwater directly into the sea. [2] [3] These systems have sparked significant environmental debate due to their impacts on marine ecosystems. [4] [5] [6]
Open loop scrubbers became widespread after the International Maritime Organization (IMO) implemented a global sulfur emissions cap in 2020. [10] They allow ships to continue using less expensive, high-sulfur heavy fuel oil while meeting air quality regulations, shifting the environmental burden from air to water. [11] [12] As of 2022, in some regions like the Baltic Sea, the number of ships fitted with these systems has quadrupled in recent years. [13] [14]
Open loop scrubbers have been subject to intense scientific scrutiny. Research shows that:
Growing concern over the environmental impact of open loop scrubbers has led to increasing regulatory restrictions. [21] [22] Many ports and jurisdictions have banned or restricted the use of open loop scrubbers in their waters, requiring ships to use either closed loop systems or compliant low-sulfur fuels instead. [23] [24] [25] [26]
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