A new study from the International Council on Clean Transportation (ICCT) found that newer Tier II machines have significantly higher nitrogen oxide (NOx) emission rates than older Tier I machines.
The study also found that there was no statistical difference in NOx emission rates between unregulated Tier 0 engines and Tier II engines. In addition to affecting tropospheric ozone, NOx also contributes to the formation of smog and acid rain.
The working paper analyzed 615 real-world NOx emissions samples from 545 ships operating in Danish waters between the North Sea and the Baltic Sea in 2019. The measurements were obtained using sensors mounted on helicopters flying into exhaust fumes.
The data includes measurements from ships covering all layers. Level I limits apply to engines on ships built between 2000 and 2010. Tier II limits apply to ships built from 2011 and are set at approximately 15-20% below Tier I. Level III is set at 80% below Level I, or approximately 75% below Level II. Level III applies to engines on ships built in 2016 or later.
In the study, the highest average NOx emissions occurred when ships were operating at less than 25% main engine load; This part of the duty cycle has been excluded from NOx compliance certification schemes for most machines.
“Together, this means that when ships are sailing slowly, such as when they are close to shore, they emit higher rates of air pollution, increasing the negative impacts of shipping on coastal air quality and human health,” the report said.
The Washington DC-based think tank is calling on the International Maritime Organization (IMO) to consider implementing non-exceeding (NTE) standards for machinery on new and existing ships, focusing particularly on operations at low loads and including a testing point.
“Clearly, the IMO approach to regulating NOx is not working as intended,” said Dr Bryan Comer, ICCT’s marine program leader. “IMO’s NOx testing cycle allows machinery manufacturers to fine-tune their machinery to pass laboratory emissions testing.” “It creates the illusion of a low-emission machine, when in reality new machines emit more air pollution than older machines.”
The opinions expressed herein are the author’s and not necessarily those of News2Sea.
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