MnrAq

96 Third IMO GHG Study 2014
Emissions
substance
Table 34 – Emissions factors for top-down emissions from combustion of fuels
Marine HFO emissions factor
(g/g fuel)
Marine MDO emissions factor
(g/g fuel)
Marine LNG emissions factor
(g/g fuel)
CO 2 3.11400 3.20600 2.75000
CH 4 0.00006 0.00006 0.05120
N 2 O 0.00016 0.00015 0.00011
NO x 0.09300 0.08725 0.00783
CO 0.00277 0.00277 0.00783
NMVOC 0.00308 0.00308 0.00301
Table 35 – Year-specific emissions factors for sulphur-dependent emissions (SO x and PM)
% Sulphur content averages – wt IMO 1
Fuel type 2007 2008 2009 2010 2011 2012
Average non-ECA HFO S% 2.42 2.37 2.6 2.61 2.65 2.51
SO x EF (g/g fuel)
Marine fuel oil (HFO) 0.04749 0.04644 0.05066 0.05119 0.05171 0.04908
Marine gas oil (MDO) 0.00264 0.00264 0.00264 0.00264 0.00264 0.00264
Natural gas (LNG) 0.00002 0.00002 0.00002 0.00002 0.00002 0.00002
PM EF (g/g fuel)
Marine fuel oil (HFO) 0.00684 0.00677 0.00713 0.00713 0.00721 0.00699
Marine gas oil (MDO) 0.00102 0.00102 0.00102 0.00102 0.00102 0.00102
Natural gas (LNG) 0.00018 0.00018 0.00018 0.00018 0.00018 0.00018
1
Source: MEPC annual reports on Sulphur Monitoring Programme.
All emissions factors are in mass of emissions per unit mass of fuel and the data compiled in Section 1.1
are in units of mass of fuel, so for oil-based fuels the production of the total emissions is a straightforward
multiplication. Further work is needed to compile the gas fuel emissions factors and the method for emissions
calculation (the units for gas fuel use are mass of oil equivalent).
2.1.2 Methane slip
Some of the fuel used in gas engines is emitted unburned to the atmosphere. This feature is specific to LNG
marine engines running on LNG with low engine loads. A new generation of gas engines, based on the Otto
cycle (spark-ignited, lean-burn engines), is reported to reduce methane slip significantly with improvements
made to cylinder, cylinder head and valve systems. In this study, methane slip is included in the combustion EF
for CH 4 in LNG-fuelled engines. However, for the top-down analysis it was not feasible to estimate the energy
usage (kWh) for the global LNG fleet.
2.1.3 Method for estimation for non-combustion emissions
Refrigerants, halogenated hydrocarbons
Refrigerants are used on board vessels for air conditioning and provisional and cargo cooling purposes.
The ozone-depleting substances (HCFCs and CFCs) have been replaced with other refrigerants, like HFCs
1,1,1,2-tetrafluoroethane (R134a) and a mixture of pentafluoroethane, trifluoroethane and tetrafluoroethane
(R404a). All these refrigerants, including the replacements for ozone-depleting substances, have significant
GWP. The GWP is reported as CO 2 equivalent (CO 2 e): this describes the equivalent amount of CO 2 that would
be needed to achieve the same warming effect. The numerical values of GWP for different substances used
in this study were taken from the IPCC Fourth Assessment Report and are based on the latest IPCC estimate
of CO 2 concentration in the atmosphere.
This part of the report builds on the findings of two others: the United Nations Environmental Programme
(UNEP) 2010 Report of the Refrigeration, Air Conditioning and Heat Pumps Technical Options Committee
and the European Commission (DG Environment) 2007 report The analysis of the emissions of fluorinated
greenhouse gases from refrigeration and air conditioning equipment used in the transport sector other than
road transport and options for reducing these emissions – Maritime, Rail, and Aircraft Sector.