In addition to SOx, ship engines emit elevated levels
of the harmful compounds of the general formula
NOx, which have negative effects that include
GHG formation in the atmosphere and damage to
respiratory health. Progressive reductions in NOx
emissions from ship engines have also been agreed
at IMO. For specified ships that operate in ECAs,58 the
strictest controls are applicable to ships constructed
on or after 1 January 2016. Such ships must produce
NOx emissions below a level known as “tier III”. For
ships operating outside such areas, tier II controls
apply.59 Unlike SOx, where emission reductions can
be achieved fairly simply, albeit at some cost, by
switching to low-sulphur fuels or installing exhaust
gas SOx scrubbers, major adjustments are needed to
ensure compliance with NOx tier III requirements.