IMSML Web Article 16/2026: Resolution MEPC.402(83) - Guidelines for Test-Bed and Onboard Measurements of Methane (CH4) and/or Nitrous Oxide (N2o) Emissions from Marine Diesel Engines

Resolution MEPC.402(83) adopted by the Marine Environment Protection Committee (MEPC) on 11 April 2025. Its origins can be traced back to MECP.377(80) on the 2023 IMO Strategy on Reduction of GHG Emissions from Ships (2023 IMO GHG Strategy) which set out the levels of ambition for the international shipping sector in rescuing GHG Emissions. Its purpose was to fuel (pardon the intended pun) the up take of zero or near-zero GHG technologies, fuels and/or energy sources. Resolution MEPC.402(83), in Annex 7, encourages stakeholders to voluntarily apply the guidelines when under taking measurements, calculation and reporting of CH4 and/or N20 emission values from marine diesel engines.

Introduction to the Guidelines

What is the purpose of the Guidelines?

To specify the protocol for test-bed and onboard measurements, calculation and reporting of methane (CH4) and/or nitro is oxide (N2O) emission values from marine diesel engines, as well as document action and verification of CH4 and/or N2O emission values, see Paragraph 1.1. These measurements and calculations should be carried out in accordance with the ‘NOX Technical Code 2008’ (as amended)(NTC2008), unless specifically provided for in Appendix 1 of the Guidelines, see Paragraph 1.2.

How are onboard measurements to be carried out?

In accordance with the Protocol set out in Appendix 1. This may be accepted for an individual engine or for an engine group  represented by the parenya engine. It should not be accepted for for an engine family without further justifications. Howver, for test bed measurements, the protocol may also be accepted for an engine family, see Paragraph 1.3.

Note, that the composition of ‘engine family’ or an ‘engine group’ are defined in NTC2008. This is set solely by affect Ong NOX emissions. These cannot be assigned to be equally applicable to CH4 and/or NO2 emissions. For liquid-to-gas fuel radio, the requirements for Highway NOX will tend to result in Lowyat CH4, see Foot note 1 to Paragraph 1.3.

What information is to be included in the CH4 and/or N2O file?

Under Paragraph 2.1, the following information is required:

[1] Details of the engine as tested, including (but not limited to the following):

[a] Model and designation;

[b] Rated power and rated speed;

[c] Listing of NO2 critical component as fitted and Settings / operating values as applied including, for CH4, NOX certified maximum liquid -to-gas fuel radioactive across load range, AND …

[d] Other component and settings / operating values which affect CH4 and/or N2O emissions.

[2] Details including draw inga of exhaustion system, showing sampling position(s);

[3] Reporting of C-slip should include crank case emission, details of how that was determined;

[4] A copy of the relevant engine test data;

Note, as given in Appendix 2 of the Guidelines and NTC 1008.

[5] Documentation on the abatement device, when a CH4 and/or N2O reducing device / system is used.

Note, when exhaust gas samples are to be drawn from both before and after the device, details of the analyser changeover arrangements and sequencing should be given if only one set of analysers is to be used.

How are CH4 and/or N2O emission values verified?

The CH4 and/or N2O file should be submitted to IMO for verification, see Paragraph 3.1. After completion of the verification, a Statement of emission values for CH4 and/or N2O should be issued by IMO in the format set out in Appendix 3 of the Guidelines, see Paragraph 3.1.

APPENDIX 1

What are the core procedures in Appendix 1?

It contains the ‘Protocol for Test-Bed and Onboard Measurements of CH4 and/or N2O Emissions from Marine Diesel Engines Based on the NOX Technical Code 2008, including the following:

[1] Test cycles and weighting factors to be applied, see Chapter 3, Paragraph 3.2;

[2] Positioning of abatement device or system, see Chapter 5, Paragraph 5.2.5.3;

[3] Permissible deviations of instruments for engine-related parameters and other essential parameters, see Chapter 5, Paragraph 5.6.1;

[4] Exhaust has temperature at the sample probe for HC, see Chapter 5, Paragraph 5.9.3.2;

[5] Test sequence, Chapter 5, Paragraph 5.9.6.2;

[6] Data Evaluation for gaseous emissions, see Chapter 5, Paragraph 5.11;

[7] Calculation of the emission mass flow rates, see Chapter 5, Paragraph 5.12.5.1;

[8] Calculation of the specific emission, see Chapter 5, Paragraph 5.12.6;

[9] Methane (CH4) analysis, see Appendix III, Paragraph 3.6;

[10] Nitrous Oxide (N2O) analysis, see Appendix III, Paragraph 3.7;

[11] Calibration of the analytical and measurement instruments, See Appendix IV;

[12] Efficiency of the non-methane cutter (NMC), see Appendix IV, Paragraph 8.5;

[13] NMC Methane Efficiency, Appendix IV, Paragraph 8.5.1;

[14] NCM Ethane Efficiency, see Appendix IV, Paragraph 8.5.2;

APPENDIX 2

What are the core provisions of Appendix 2?

Two things: Engine test report and test data. In particular, CH4 and/or N@O calculations, including the following:

[1] Engine details, for example:

[a] Manufacturer;

[b] Engine type;

[c] Emission abatement device;

[d] Engine family or engine group identification;

[e] Serial number;

[f] Rated power;

[g] Rated speed.

[2] Emission test results, for example:

[a] Test cycle;

[b] C(fCH$) weighted;

[c] C(slip-CH4) weighted;

[d] N@O (weighted);

[e] Test identification;

[f] Date / time;

[g] Test site;

[h] Test number;

[i] Company;

[j] Date and place of report;

[k] Signature.

[3] Measurement equipment and analyser, for example:

[a] Manufacturer;

[b] Model;

[c] Measurement ranges;

[d] Calibration.

[4] Liquid fuel characteristics, for example:

[a] Type;

[b] Properties;

[c] Elemental analysis.

[5] Gas fuel characteristics, eg gas emissions data.

[6] Engine parameters to be measured and recorded, eg mode, engine data and ambient data.

APPENDIX 3

What forms the core of Appendix 3?

It contains the form of statement of emission values for Methane (CH4) and/or Nitrous Oxide (N2O). This is issued in accordance with the ‘Guidelines’ pursuant to MEPC.402(83) by the authority of the named government acting on the authority of IMO.

What particulars of the applicant are required for this form?

[1] Engine manufacturer and model;

[2] Engine serial number;

[3] Abatement device manufacturer and model;

[4] Device serial number;

[5] Applicable test cycle(s);

[6] C(CH4) in g/kg fuel;

[7] C(slip-CH4) percentage (of the mass of the methane containing fuel used by the engine);

[8] C(fN2O) in g/kg fuel.

ANNEX 8 - Work Plan for the Development of a Regulatory Framework for the Use Onboard Carbon Capture and Storage (OCCS)

What is the goal of Annex 8?

To develop a regulatory framework for the use of onboard carbon capture and storage (OCCS). This is intended to aid reduction in net GHG emissions from ships without negatively affecting the environment.

What are the Objectives of the Work Plan?

There are 5 identified objectives in Annex 8:

[1] Avoiding emissions to air and discharges to sea that are harmful to the environment and ensuring traceability of the captured carbon;

[2] Consider legal barriers that may hinder the use of OCCS and transportation and transfer of the captured carbon to safe permanent storage or utilization;

[3] Facilitate access to certified reception facilities for the value chain for permanent storage or utilization of captured carbon;

[4] Enable recording and reporting of relevant data; and … … …

[5] Develop options that take into account GHG emission reductions from onboard carbon capture in the IMO GHG regulatory framework.

What are the boundaries (ie Freedoms and Constraints)?

[1] Addressing issues relating to health, safety and the human element;

[2] Addressing issues relating to accounting of emissions from ships using OCCS;

[3] A technology-neutral approach to regulatory framework;

[4] Environmental risks have to be considered by the legal framework;

[5] Take into consideration short-term and mid-term GHG reduction measures.

What are the ‘TASKS’ contained in Annex 8?

There are 5 main tasks:

[1] Avoiding emissions to air and discharges to the sea that are harmful to the environment, as well as ensuring traceability of the captured carbon;

[2] Consider legal barriers that may hinder the use of OCCS and transportation as well as transfer of captured carbon to safe permanent storage or utilisation;

[3] Facilitate access to certified reception facilities for the value chain for permanent storage or utilisation of captured carbon;

[4] Enabling recording and reporting o relevant data;

[5] Develop options that take into account GHG emission reductions from onboard carbon capture in IMO regulatory framework.

Thank you for reading IMSML Web Article 16/2026

Stay tuned for the next IMSML Web Article 17/2026: Malaysian Shipping Notice (MSN) 06/2025 Introducing Resolution MEPC.403(83) - Amendments to the 2022 Guidelines on Survey and Certification of the Energy Efficiency Design Index (EEDI)

Signing-off for today,

Dr Irwin Ooi Ui Joo, LL.B(Hons.)(Glamorgan); LL.M (Cardiff); Ph.D (Cardiff); CMILT

Professor of Maritime and Transport Law

Faculty of Law

Universiti Teknologi MARA Shah Alam

Selangor, Malaysia

Tuesday,  21 April 2026

Note that I am the corresponding author for the IMSML Website Articles. My official email address is: uijoo310@uitm.edu.my