New NOx limits are entering to force
With MARPOL VI (2008)/13.4 operation of a marine diesel engine is only permitted when its emission of nitrogen oxides (NOx) is within certain limits (meeting Tier II engines), depending on the rated engine speed (crankshaft revolutions per minute). This applies to newbuildings with the keellaying date between 01st of January 2011 and 01st of January 2016. (MARPOL VI (2008)/13.4, MEPC 176(58))
Application date for the above is January 1st of 2011 as new MARPOL amendments are entering to force.
Source: Safety4Sea