Tier III NOx

Tier III is the strictest IMO limit on nitrogen oxide emissions from marine diesel engines, cutting allowable NOx to about 80% below Tier I. It applies only to ships built from 2016 onward while operating inside designated NOx emission control areas, currently the North American and US Caribbean areas and, for newer builds, the Baltic and North Sea. Engines meet it with selective catalytic reduction using a urea reductant or with exhaust gas recirculation.