Compliance with new MARPOL and local regulations is a constant driver for emission control technologies and added to that complex mix are the advent of new fuels aimed at solving one problem but bringing new challenges of their own. 

It is difficult to imagine that just twenty-five years ago – the average lifetime of a modern ship – shipowners and operators did not have to worry about what mix of gases and compounds was being discharged into the atmosphere from the exhaust stacks.  

For sure, the IMO had promulgated the first regulations on NOx in 1997, but they only applied to ships built after 1 January 2000 and had been well trailed so that most engine makers had developed engines that could meet them without any additional technology. The Tier II NOx regulation limits only became effective in 2011 and are currently in force globally except where NOx ECAs have been established and where Tier III levels will apply in accordance with the various coming into effect dates.