How to calculate carbon dioxide equivalent emissions from different GHG sources?

Green House Gases (GHGs) are those that can absorb and emit infrared radiation. There are six Green House Gases as identified under the Kyoto protocol. These are:- Carbon dioxide (CO₂), Methane (CH₄), Nitrous oxide (N₂O), Hydrofluorocarbons (HFCs), Perfluorocarbons (PFCs); and Sulphur hexafluoride (SF₆). While creating the GHG inventory of the organization, there is a need to calculate all the six GHGs e.g. GHG emissions from the burning of fossil fuels, methane emission from anaerobic digestion of organic matter (Spent wash treatment in anaerobic digester in molasses based distillery), CO₂ emission from use of fire extinguishers during actual fire conditions or emergency preparedness programs/training in the organization, etc.

Clause 4.3.3 of ISO 14064-1 specifications suggests that organization shall select and use quantification methodologies that will reasonably minimize uncertainty and yield accurate, consistent and reproducible results. ISO 14064-1 specifies that organization shall calculate their GHG emission as per six greenhouse gases separately. The same method is given in following schematic;

Therefore, whatever the source of Green House Gasses and the calculation methodology, the resulting value should be in mass unit of Carbon dioxide equivalent form. By multiplying the resulting value of gas other than CO₂ with the respective Global Warming Potentials (GWP) will result in CO₂ equivalent form. The concept of global warming potential (GWP) has been developed in order to enable comparison of the ability of different GHGs to trap heat in the atmosphere (Read more on GWP here). Following table shows GWP of different GHGs;

GHGs	GWP
Carbon dioxide CO2	1
Methane CH4	21
Nitrous oxide N2O	310
Sulphur hexafluoride SF6	23900
HFC	Click here
PFC	Click here

Following examples will provide calculation methods as per the GHG protocol and ISO 14064-1;

Example 1: GHG emission from the burning of diesel in stationary source i.e. DG sets.

Burning of fuel in stationary source emits Methane and Nitrous oxide. To understand the further calculation process, let’s take 100 liters of diesel consumption in the DG set. The calculation would be;

1. CO₂ emission = Fossil fuel consumption in volume unit  X  CO₂ emission factor (Ton per volume unit)
2. CH₄ emission = Fossil fuel consumption in volume unit  X  CH₄ emission factor (Ton per volume unit)
3. N₂O emission = Fossil fuel consumption in volume unit  X  N₂O emission factor (Ton per volume unit)

Total GHG emission (in tCO₂ eq) = (CO₂ emission) + (CH₄ emission X 21) + (N₂O emission X 310)

1. CO₂ emission  = 100 X 0.00265
2. CH₄ emission = 100 X 0.00000036
3. N₂O emission = 100 X 0.000000021

Total GHG emission (in tCO₂ eq) = 0.265299393 + (0.000035819 X 21) + (0.00000215 X 310)

Total GHG emission (in tCO₂ eq) = 0.2667

Example 2: GHG emission from the use of R-134a [HFC – C₂H₂F₄ (CH₂FCF₃)] from the air conditioning system

Conventional air conditioning systems uses HFC based referents which might leak HFC gas into the atmosphere. Let’s consider 100 kg of HFC leaked from the air conditioning systems, then how can we calculate GHG emission in CO₂ equivalent form? The answer is here;

R-134a (HFC) = 100 Kg

Global Warming Potential of R-134a = 1300 t CO_{2 e} per ton of R-134a

Total GHG emission (in tCO₂ eq) = (100/1000) X 1300

Total GHG emission (in tCO₂ eq) =   130

Note: For GHG emission factors, please refer IPCC GHG EF database