Newer ship engines emit more NOx than older engines - ICCT

A study conducted by the International Council on Clean Transportation (ICCT) has shown that newer Tier II ship engines emit considerably more nitrogen oxide (NOx) compared to older Tier I engines.

PHOTO: Cranes ready to unload a container ship in Port of Long Beach. Getty Images

The study analysed 615 samples of real-world NOx emissions obtained from 545 ships operating in Danish waters between the North Sea and the Baltic Sea in 2019.

To measure the NOx emissions, ICCT used exhaust gas sampling devices, also known as sniffers. They were attached to helicopters and flown into the exhaust flumes of ships as they sailed. The data collected included measurements from ships with different engine tiers, it said.

The study indicate that NOx is responsible for smog and acid rain, and also has an impact on tropospheric ozone. The research revealed that newer Tier II engines had significantly higher NOx emission rates compared to older Tier I engines.

Additionally, they found that there is no significant difference in NOx emission rates between Tier 0 engines and Tier II engines. This implies that Tier II engines, despite being subject to emission regulations, had similar NOx emission levels as the older, unregulated Tier 0 engines.

The highest average NOx emissions were recorded when ships operated at less than 25% of their main engine load. This suggests that during low-load conditions, ships tend to emit higher levels of NOx. ICCT says this specific part of the duty cycle is not covered by NOx compliance certification schemes for most engines.

ICCT has asked the International Maritime Organization (IMO) to establish not-to-exceed (NTE) standards for engines on new and existing ships. These standards should focus on operations at low loads, including a test point below 25% load. The ICCT's report states that the IMO's current approach to regulating NOx is not effective and that newer engines are emitting more air pollution than their older counterparts.

“Clearly, IMO’s approach to regulating NOx isn’t working as intended,” ICCT’s marine program lead Dr Bryan Comer said. “IMO’s NOx test cycle allows engine manufacturers to fine-tune their engines to pass the emissions test in the laboratory, creating the illusion of a low-emission engine. In reality, newer engines are emitting more air pollution than older engines,” he added.

The study's findings highlight the need for continued efforts to reduce emissions from ships, which are a significant contributor to air pollution and its negative impacts on coastal air quality and human health, Comer said.

By Debarati Bhattacharjee

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