MnrAq

120 Third IMO GHG Study 2014
• SO x – The modelled Third IMO GHG Study 2014 SSD Tier 0 MDO emissions factors are 74% lower
owing to use of the annual average IMO published fuel sulphur contents (0.15% for 2007) in the Third
IMO GHG Study 2014 compared to the 0.5% used in the Second IMO GHG Study 2009.
• PM – the modelled Third IMO GHG Study 2014 SSD Tier 0 MDO emissions factors are 13% higher
owing to use of fuel correction factors as described in Section 2.2.7 and Annex 6 compared to the
value developed in the Second IMO GHG Study 2009.
• CO – The Third IMO GHG Study 2014 SSD Tier 0 HFO emissions factors are 63% lower than the
Second IMO GHG Study 2009. The 2009 study used CORINAIR emissions factors for CO, which can
be traced back to the Lloyd’s Register report Marine Exhaust Emissions Research Programme (1995).
The Third IMO GHG Study 2014 used an updated CO emissions factor that was recently supported
in the Kristensen (2012) report.
• CH 4 – The Third IMO GHG Study 2014 SSD Tier 0 HFO emissions factor is 80% lower than the
Second IMO GHG Study 2009. The 2009 study used the IPCC 2013 emissions factor for CH 4 , which
can be traced back to the Lloyd’s Register report Marine Exhaust Emissions Research Programme
(1995). The 2014 study used an updated CH 4 emissions factor. In addition to the CH 4 combustion
product, methane is also released into the atmosphere as an unburnt fuel from engines operating on
LNG Otto-cycle engines. In this report, the methane slip has been included in the methane emission
inventory and an additional non-combustion emissions factor has been assigned for CH 4 to account
for this feature. For further details, see Section 2.2.6.
• N 2 O – The Third IMO GHG Study 2014 SSD Tier 0 HFO emissions factor is two times higher than the
Second IMO GHG Study 2009. The 2009 study used CORINAIR emissions factors for N 2 O, which
can be traced back to the Lloyd’s Register report Marine Exhaust Emissions Research Programme
(1995). The IPCC guidelines state that the uncertainty of the emissions factor is as high as 140%. The
Third IMO GHG Study 2014 used an updated N 2 O emissions factor.
• NMVOC – The Third IMO GHG Study 2014 SSD Tier 0 HFO emissions factor is 28% higher than
the Second IMO GHG Study 2009. The 2009 study used CORINAIR emissions factors for NMVOC,
which can be traced back to Lloyd’s Register report Marine Exhaust Emissions Research Programme
(1995). The Third IMO GHG Study 2014 used an updated NMVOC emissions factor.
2.4.2 QA/QC of top-down emissions factors
The top-down emissions factors (Table 34, Section 2.1.1) are a subset of the bottom-up emissions factors and
were selected as described in Section 2.2.7. They have the same correlations to the Second IMO GHG Study
2009 as presented in Section 2.4.1.
2.4.3 Comparison of top-down and bottom-up inventories
Top-down and bottom-up time series for each pollutant inventory are presented in Figure 75 and Figure 76
respectively. These results are provided with the same units and similar (but not identical) scales for visual
comparison.
One clear difference is the trend pattern across years for some pollutants. For example, the top-down data
among all pollutants remains similar. Most top-down inventories reveal a decline after 2007, to 2009 or
so, and an increase in subsequent years. This can be explained because the top-down data do not include
technology detail and the inventories are therefore computed using a best-judgement fleet-average emissions
factor. Conversely, the bottom-up inventories can exhibit diverging patterns from one another and very
different patterns from the top-down inventory trends. Whereas CO 2 in the bottom-up results exhibits a trend
similar to SO x , NO x and PM, the pattern for CH 4 is increasing over the years. This is because the number of
larger vessels using LNG has increased, despite the fact that top-down statistics have not begun reporting any
LNG in international sales statistics.