Frequently Asked Questions

Emission Factors questions (17)

• General(3)
• Road Transport(7)
• Other Transport(3)
• Other Sectors(4)

Emissions questions (21)

• General(7)
• Road Transport(8)
• Other Transport(3)
• Stationary Combustion and Part A and B processes(3)

Mapping questions (4)

Units and Abbreviations questions (7)

If emissions are reported in kt of C how can this be converted into kt of CO₂?

To convert from kt of CARBON (C) to kt of Carbon Dioxide (CO₂)multiply by 3.6666667 or 44/12.

How can I convert NOx to N0₂

There is no set percentage of NOx that is NO₂. Both NO₂ and NOx are emitted from combustion, but the split depends on the combustion conditions. Traditionally the rule of thumb has been that 5% of NOx is emitted as primary NO₂, which is probably reasonable for most combustion sources and petrol traffic. Diesel is higher ~12% up to Euro 2 and much higher from Euro 3. See the recent AQEG report for more information.

What is meant by the number 2.5e-04 kilotonne/Mth?

The emission factors you quote above are provided in exponential notation. In this format, one million which has 6 zeros is the same as 10 to the power of 6 or as on scientific calculators and in the NAEI emission factor database this is written 1E6. Therefore 2.5E-04 for example is the same as 0.00025. The emission factors that you quote are provided in terms of x kilo tonnes of emissions per million therms of gas consumed.

I have for a boiler the gas oil throughput figures in litres. How can I convert this to the units required by the emissions factors database (kilo tonnes)?

To go from gas oil in litres to tonnes, please see the DTI's Digest of United Kingdom Energy Statistics. The latest version can be found at here.

What does VOC stand for?

VOCs are volatile organic compounds. They are a collection of organic compounds which differ widely in their chemical composition but display similar behaviour in the atmosphere. The diversity of processes which emit VOCs is huge, covering industry, transport, agriculture and domestic sources. The inventory reports NMVOCs (non methane VOCs). For further information please refer to the NAEI home page and select non methane VOCs from the drop down list.

Is the unit 'Mth' is different to 'mth'? and 'Mth' is in any way related to 'calories' or 'Joule' and if yes in what way?

A Mth is a megatherm or a million therms, a mth is a millitherm or a thousandth of a therm. The European Union's definition of a therm is 105.5060 mega joules. The Americans use a slightly different definition. A therm is also equal to 25200 kcals.

What is the fuel 'Derv'?

DERV is diesel fuel used in road vehicles; from d(iesel) e(ngine) r(oad) v(ehicle).