National Atmospheric Emissions Inventory

Appendix 2

The Methodology of the National Atmospheric Emissions Inventory


1 Introduction

 This Appendix describes the methodological changes made to the NAEI since the 1995 Inventory.

2 Reporting Format

 In the new inventory the UNECE/CORINAIR SNAP 94 system of classification has been adopted. This is an internationally recognised system of reporting emission inventories and is used by EMEP and UNECE. It supersedes CORINAIR SNAP 90 system used in previous inventories. The CORINAIR SNAP 94 format reports data in upwards of 393 categories each with its own definition. The tables in this report only report the 'top tier' of eleven categories with some additional detail. Although CORINAIR SNAP 94 uses 11 categories like CORINAIR SNAP 9O, the definitions of some of them have changed so it has been necessary to reclassify a number of sources particularly in industry and energy transformation. It should be noted that the classification system cuts across economic sectors so that:


are reported in separate categories, even though they may occur in the same economic category.

Table B1 summarises the new classifications. A number of changes have been made to the inventory in adopting this format and these are discussed below.

2.1 Combustion in Energy Production and Energy Transformation (01)

 This now contains combustion emissions from public power generation, refineries, coke ovens, collieries, gas production, nuclear-fuel production, solid smokeless fuel production, offshore fuel consumption. Process emissions from refineries (SO2 from catalytic crackers), coke ovens, SSF production are reported under 04 Production Processes.
The emissions reported for public power have changed slightly because a proportion of this gas generation capacity has been identified as industrial generation or generation for transport



Table B1 Emission Source Classification

  UNECE/CORINAIR SNAP 94 Source Category Main Sources
01 Combustion in Energy Production and Transformation  
  Public Power Public power plants including municipal solid waste and biogas combustion
  Petroleum Refining Plants Petroleum refineries combustion
  Other Combustion. & Transformation Combustion in smokeless fuel plant, collieries, oil and gas plant, offshore industry (not flaring)
02 Comb. in Commercial/Institutional/Residential/Agriculture  
  Domestic Combustion in residential plant, including domestic boilers and fires.
  Other Commercial and institutional plants; plants in agriculture, forestry and aquaculture.
03 Combustion in Industry  
  Iron & Steel Iron and steel reheating furnaces, sinter plant, foundries
  Other Industrial Combustion Industrial combustion plants: furnaces: industrial production
04 Production Processes Processes in petroleum, iron and steel, non-ferrous metal, chemical, wood, food, drink and other industries.
05 Extraction./Distribution of Fossil Fuels Extraction of solid, liquid and gaseous fossil fuels; including off-shore activities (apart from gas flaring); liquid fuel, gasoline and gas distribution.
06 Solvent Use Paint application; degreasing; chemical products manufacturing or processing; other use of solvents.
07 Road Transport Passenger cars; light and heavy duty vehicles; mopeds; motorcycles; gasoline evaporation from vehicles; tyre and brake wear
08 Other Transport & Machinery  
  Military Military aircraft and naval vessels; military machinery (military road vehicles are included in road transport)
  Railways Railway locomotives
  Shipping Inland waterways, boats, domestic navigation.
  Civil Aircraft Domestic and international ground movement and take off and landing cycles up to 1 km from the airport.
  Off-Road Agricultural machinery; gardening, construction and aircraft support equipment; mobile industrial equipment powered by diesel or petrol engines.
09 Waste Treatment & Disposal Incineration of domestic and industrial waste; off-shore gas flaring; other waste treatment
10 Agriculture/Forestry/Land Use Change Culture with and without fertilisers; stubble straw burning; enteric fermentation and manure management of animals; managed forests
11 Nature NMVOC emissions from managed and unmanaged forests only


undertakings. This is now reported under 02 and 03 respectively. Municipal solid waste incineration where electricity is generated has been added to the Public Power estimates. These emissions were previously reported as waste disposal.

2.2 Combustion in Commercial, Institutional, Residential, Sectors and Agriculture, Forestry and Aquaculture. (02)

 The main changes here are the transfer of stationary combustion in agriculture and railways from the old agriculture and railways categories. Also the emission from electricity generation for transport is now reported here.

2.3 Combustion in Industry (03)

 The main change here is the transfer of industrial gas generation from the old power stations category. Also the transfer to 01 of fuel combustion emissions of coke production, SSF production, gas production and nuclear fuel production. Emissions of carbon dioxide from cement kilns, lime kilns and glass production resulting from the degradation of limestone are now classified as process emissions in 04.

2.4 Production Processes (04)

 The CORINAIR SNAP 94 instructions give precise details of what should now be reported here. The category used to include SO2 from sulphuric acid; NOx and N2O from nitric acid production; N2O from adipic acid manufacture and NMVOC from the petroleum and organic chemical industries. The category now contains emissions of CO2 from limestone use in cement kilns, glass production, iron & steel industry. Process emissions transferred from the old Industry category include process emissions from coke ovens, SSF plant, blast furnaces, SO2 emissions from catalytic crackers in refineries and CO2 emissions from ammonia production. In addition, emissions from electric arc furnaces used in the iron and steel industry and the CO2 emission from soda ash use in glass making, which have not been included in previous inventories are reported here. For PM10, Production Processes includes Iron & Steel blast furnaces, Flaring of blast furnace gas and coke oven gas, quarrying, construction and general dust producing processes in industry.

2.5 Extraction and Distribution of Fossil Fuels (05)

 This contains fugitive emissions such as methane emissions from coal mining, leakage from the gas transmission system, venting on offshore installations, and evaporative losses of NMVOC in the extraction and distribution of petroleum products. Offshore flaring has been transferred to 09.


2.6 Solvent and Road Transport (06 & 07)

 There have been no classification changes.

2.7 Other Mobile Sources and Machinery (08)

 As in the previous inventory this category covers emissions from aircraft, shipping, railways, military and other off-road machinery used in agriculture, industry and gardening.

There have been some minor changes. The railways estimate refers only to locomotives - stationary combustion in the railway sector is reported under 02.

Under CORINAIR SNAP 94, emissions from international shipping within ports are no longer reported. Hence shipping only covers fishing, inland waterways, coastal shipping and the offshore industry marine transport. Naval vessels are reported under military. This should result in significant reductions in the national totals, i.e. 514 kt Carbon, 23 kt SO2, 36 kt NOx and minor reductions i.e. 0.046 kt CH4 , 3.6 kt NMVOC, 0.9 kt Black Smoke, 5.7 kt Carbon Monoxide and 2 kt PM10.

As a result of the removal of international shipping it has been necessary to modify the final user table. Emissions from the production and refining of the fuel oils sold into marine bunkers have been moved from water transport to a new category 'Exports and Marine Bunkers'.

2.8 Waste Treatment and Disposal (09)

 As previously this category contains emissions waste incineration, methane from landfill and sewage treatment. However, emissions from waste incinerators that are used to generate electricity have been transferred to 01. Waste incineration emissions where there is no generation remain in 09. The main change is the transfer of offshore flaring from the old category Extraction and Distribution of Fossil Fuels into this category.

2.9 Agriculture (10)

 This reports emissions from the use of fertilisers, liming of soils, methane from livestock and their wastes and emissions from stubble burning (banned since 1993). The fuel combustion emissions previously reported in the old agriculture category are now reported under 02.

2.10 Nature (11)

This is unchanged and relates to NMVOC emissions from managed and unmanaged forests.


3 Methodological Changes in the Estimates

3.1 Greenhouse Gases

 3.1.1 Carbon Dioxide

There have been a number of significant changes in the methodology of the carbon dioxide estimates since the 1995 Inventory. These are:

  1. The new inventory now takes account of the combustion of unrefined or sour natural gas burnt in a thermal power station. This has a higher carbon content than mains gas and has resulted in an overall increase of 243 kt carbon .

  2. Emissions from the combustion of unrefined natural gas used in the offshore industry have been revised based on recent data from UKOOA(1997). This has resulted in an increase of around 581 kt carbon in 1995 due to an increase in the estimated carbon content of the gas used.

  3. Emissions from the combustion of crude oil and gas during well testing were estimated based on UKOOA(1997). The new source is a significant contributor at 161 kt carbon in 1995.

  4. Offshore flaring emissions have been revised slightly based on UKOOA (1997). More precise data on the gas carbon content has resulted in an increase of 23 kt carbon emitted.

  5. Carbon dioxide emissions from blast furnaces are still calculated from a mass balance on the coke consumed and the blast furnace gas produced. Modifications to the methodology take account of blast furnace gas flaring and the carbon sequestrated in the steel produced. Emissions from limestone and dolomite used in blast furnaces are also included. The change has resulted in a small reduction of around 21 kt carbon from blast furnaces. This emission is now reported in the in production processes.

  6. Emissions from a new source, electric arc furnaces have been included. These are based on EMEP/CORINAIR(1996) methodology. The emission at 16 kt carbon is small and other emissions are insignificant.

  7. Emissions from aluminium production have been included for the first time. These are based on IPCC (1997) Guidelines and data provided by manufacturers. Emissions of carbon dioxide are significant at 101 kt carbon.

  8. Emissions from the combustion of waste oils and scrap tyres in cement kilns are now included. The proportion of these fuels burnt is still quite small and only results in an increase in carbon emissions of 94 kt in 1995.

  9. Under the new CORINAIR SNAP 94 reporting guidelines, emissions from international shipping are no longer included in the National Total. This has resulted in a large reduction of 514 kt in the carbon total.

Methane

  1. The new inventory includes a tiny methane emission from farmed deer both from enteric fermentation and animal wastes. More importantly, however, emissions from lambs have been estimated separately from adult sheep using a lower factor. This has resulted in a decrease of around 52 kt CH4 in the total sheep emission.

  2. Emissions from the offshore oil and gas industry have been extensively revised based on a new study by UKOOA (1997) of offshore emissions in 1995 and a revision of the UKOOA(1993) study for 1991. The main change has been to calculate emissions from flaring, natural gas use, venting, well testing and fugitive emissions separately. Venting is the main source of methane and total offshore emissions have decreased by 18 kt in 1995.

  3. Emissions of methane from municipal waste incineration have been revised downwards based on Environment Agency (1997) data which show emissions to be insignificant.
Nitrous Oxide

  1. The most important revision has been to emissions reported under agricultural soils. In the previous inventory, only emissions of nitrous oxide from the application of fertilisers to soils and the cultivation of legumes were estimated. In the new Inventory, the Revised 1996 IPCC Guidelines methodology has been used for these sources and additional sources estimated . Thus the sources included under agricultural soils are :
    • Cultivation of legumes
    • Fertiliser application
    • Crop residues
    • Cultivation of histosols
    • Improved grass
    • Grazing animal wastes
    • Manure used as fertiliser
    • Leaching
    • Atmospheric deposition of NH3 and NOx

  2. As a result of the increased IPCC emission factors and the new sources reported, emissions from agricultural soils have increased from 6.2 to 93 kt N2O in 1995. The most significant sources are fertiliser application and leaching at 26 and 27 kt N2O respectively.
  3. There has been a significant revision of nitrous oxide emissions from the treatment of animal wastes. The new estimates are based on the Revised 1996 IPCC Guidelines (IPCC, 1997) but with UK data for the distribution of waste management systems and the waste production per head. The revision has resulted in a modest increase in emissions from 3.5 kt to 5 kt N2O in 1995.

  4. The emission factor for Combined Cycle Gas Turbine power stations has been revised downwards based on new data (Stewart, 1997). Also some gas consumption has been identified as being burnt in conventional boilers. This has resulted in an overall reduction of 2.7 kt N2O.

Industrial Gases: HFC; PFC; SF6

  1. There has been virtually no change except the tables are based on a more precise dataset. Hence estimates are quoted more precisely so that PFC emissions from PFC manufacture which were included previously, are now identified.

  2. There has been a revision of emissions from firefighting: it is now assumed that 50% of fluids used are PFC and the rest HFC.

3.2 Acidifying Gases

 Nitrogen Oxides

  1. Emissions from the offshore oil and gas industry have been extensively revised based on a new study by UKOOA (1997) of offshore emissions in 1995 and a revision of the UKOOA(1993) study for 1991. The main change has been to calculate emissions from flaring, natural gas use, venting and well testing separately. Emissions from flaring and gas consumption are the most important sources of NOx. The new study shows that NOx emissions from flaring are significantly lower than previously thought and this is largely responsible for an overall decrease of 64 kt NOx.

  2. Under the new CORINAIR SNAP 94 reporting guidelines, emissions from international shipping are no longer included in the national total. This has resulted in a 36 kt reduction in the NOx total in 1995.

  3. Emissions from road transport have been revised to take account of new COPERT 2 emission factors for NOx , CO and NMVOC and new data on the age distribution of heavy goods vehicles. This has resulted in a reduction in NOx emissions of 32 kt.

  4. Emissions from blast furnaces are now estimated on the basis of EMEP/CORINAIR (1996) emission factors for blast furnace charging resulting in a reduction of around 24 kt NOx .

  5. An improved estimate has been made of the high NOx emissions from reformers used on ammonia plant based on manufacturer's data. The 1995 emission was around 4.4 kt NOx.

  6. Emissions from a new source, electric arc furnaces have been included. These are based on EMEP/CORINAIR(1996) methodology. The emission at 0.9 kt NOx is small.

  7. Emissions from aluminium production have been included for the first time. These are based on IPCC (1997) Guidelines and data provided by manufacturers. Emissions of NOx are insignificant at 0.5 kt NOx in 1995

Sulphur Dioxide

  1. Under the new CORINAIR SNAP 94 reporting guidelines, emissions from international shipping are no longer included in the national total. This has resulted in a 23 kt reduction in the SO2 total in 1995.
  2. Emissions from the offshore oil and gas industry have been extensively revised based on a new study by UKOOA (1997) of offshore emissions in 1995 and a revision of the UKOOA(1993) study for 1991. The main change has been to calculate emissions from flaring, natural gas use, venting and well testing separately. Emissions from flaring and gas consumption are minor and are lower than previous estimates at 0.8 kt SO2 . However the addition of the new source, well testing has resulted in an increase of 6 kt SO2.

  3. Emissions from a new source, electric arc furnaces have been included. These are based on EMEP/CORINAIR(1996) methodology. The emission at 0.6 kt SO2 in 1995 is small.

  4. Emissions from aluminium production have been included for the first time. These are based on IPCC (1997) Guidelines and data provided by manufacturers. Emissions of sulphur dioxide are significant at 3.6 kt SO2 in 1995

  5. Wastage of coke oven gas has been included for the first time. This results in a small emission of 1.6 kt SO2 from flaring in 1995.

  6. Emissions from the combustion of waste oils and scrap tyres in cement kilns are now included. The proportion of these fuels burnt is still quite small and only results in an increase in SO2 emissions of 2.2 kt in 1995.

  7. At the end of 1996 all municipal solid waste incinerators will have to comply with new emission standards. As a result a number of old incinerators have closed down; some have been renovated and some new ones opened. Emissions from 1995 onwards have been revised based on data reported in the CRI. The changes have resulted in a decrease of 2.2 kt SO2 in 1995. Some of these incinerators are now classified as public power since they generate electricity for the public supply.

  8. A new source, incineration of sewage sludge has been included. This contributed 1 kt SO2 in 1995.

3.3 Toxic Pollutants

 Carbon Monoxide

  1. Emissions from road transport have been revised to take account of new COPERT 2 emission factors for CO and new data on the age distribution of heavy goods vehicles. This has resulted in a reduction in carbon monoxide emissions of 513 kt in 1995.

  2. Emissions from coal fired power stations have been revised to take account of the lower emissions of CO from low-NOx burners. This has reduced emissions by 48 kt CO in 1995. Conversely emissions from combined cycle gas turbines have been revised upwards to reflect emission data in the CRI (Environment Agency, 1997). Overall emissions from power generation have reduced by 30 kt CO in 1995.

  3. Emissions from aluminium production have been included for the first time. These are based on IPCC (1997) Guidelines and data provided by manufacturers. Emissions of CO are significant at 22 kt CO in 1995.
  4. Emissions from the offshore oil and gas industry have been extensively revised based on a new study by UKOOA (1997) of offshore emissions in 1995 and a revision of the UKOOA(1993) study for 1991. The main change has been to calculate emissions from flaring, natural gas use, venting and well testing separately. Emissions from flaring and gas consumption are the most important sources of NOx.. The new estimate is 8 kt lower than previous in inventories.

  5. Under the new CORINAIR SNAP 94 reporting guidelines, emissions from international shipping are no longer included in the National Total. This has resulted in a 6 kt reduction in the NOx total in 1995.

  6. Emissions from a new source, electric arc furnaces have been included. These are based on EMEP/CORINAIR(1996) methodology. The emission at 4 kt CO is small.

  7. Process emissions from blast furnaces are now estimated on the basis of EMEP/CORINAIR (1996) emission factors for blast furnace charging. Also emissions from blast furnace gas combustion have been revised upwards. These changes have had negligible effect on the total CO emission.

NMVOC

  1. Emissions from road transport have been revised to take account of new COPERT 2 emission factors for NOx , CO and NMVOC and new data on the age distribution of heavy goods vehicles. This has resulted in reductions in NMVOC emissions of 11 kt in 1995.

  2. A further evaporative emission of 3 kt from the distribution of gasoline has been added. Evaporative emissions from marketing and retail storage and road tankers were in previous inventories but now include dispatch from refineries.

  3. Emissions of NMVOC from municipal waste incineration have been revised downwards based on Environment Agency (1997) data which show emissions to be insignificant.

  4. Emissions from the offshore oil and gas industry have been extensively revised based on a new study by UKOOA (1997) of offshore emissions in 1995 and a revision of the UKOOA(1993) study for 1991. The main change has been to calculate emissions from flaring, natural gas use, venting, tanker loading and well testing separately. Emissions from tanker loading, venting and fugitives are the most important sources of NMVOC. The overall emission from offshore activities for 1995 is down by 26 kt since last year's inventory with the main reduction being in fugitives and flaring.

  5. There have been minor revisions in the solvents estimates mainly due to some new survey data by Local Authorities and additional data from solvent suppliers. The 1995 estimate has been reduced by 84 kt NMVOC.

  6. The emissions from chemical and other industrial processes have been reduced by 28 kt based on new data derived from the CRI (Environment Data, 1997) and manufacturers own estimates.
  7. Under the new CORINAIR SNAP 94 reporting guidelines, emissions from international shipping are no longer included in the national total. This has resulted in a 4 kt reduction in the NNVOC total in 1995.

PM10

  1. "Combustion in Energy Production and Transformation", "Public Power" now includes emissions from the combustion of MSW (~ 21kt) Emission factors used are from (EP42).

  2. Estimates for coal and oil fired stations have been revised based on the reported emissions of "dust" from coal and oil use in power stations and an assumed 67% PM10 from USEPA work described in AP42 Vol 5.

  3. Estimates for Combustion in Energy Production and Transformation, Other Combustion and Transformation includes ~21kt from Coke production previously assigned to Iron and Steel (see Digest 19).

  4. Domestic emissions have increased in comparison to last years dataset due to revisions to the PM10 emission factors for Anthracite and SSF from 2.6 to 3.59 and 2.75 to 5.6 respectively.
  5. Refinery emissions have been reduced due to emission factor revisions for fuel oil. (from 2.85 to 1.032)

  6. "Other Transport and Machinery" "shipping" now excludes "Other UK Shipping" (Bunker) emissions (~2.2kt) as required by UNECE and CORINAIR94.

Black Smoke

  1. At the end of 1996 all municipal solid waste incinerators will have to comply with new emission standards. As a result, a number of old incinerators have closed down; some have been renovated and some new ones opened. Emissions from 1995 onwards have been revised based on data reported in the CRI. The changes have resulted in a decrease of 38 kt black smoke in 1995. Some of these incinerators are now classified as public power since they generate electricity for the public supply.

  2. Emissions from diesel powered road transport have been revised to take account of data on the age distribution of heavy goods vehicles. This has resulted in a reduction in black smoke emissions of 25 kt in 1995.

  3. Under the new CORINAIR SNAP 94 reporting guidelines, emissions from international shipping are no longer included in the national total. This has resulted in a 1 kt reduction in the black smoke total in 1995.

Heavy Metals

  1. The main methodological change in the 1996 Inventory is in the estimation of power generation emissions. The emissions from coal and oil fired plant are based on the Power Generators own estimates for England and Wales and have been extrapolated to the United Kingdom based on fuel consumption data for Scotland and Northern Ireland. As a result of these changes, there have been significant increases in emissions from mercury, nickel, chromium, lead, copper and cadmium and reductions in emissions of arsenic, selenium and vanadium.

  2. At the end of 1996 all municipal solid waste and clinical incinerators had to comply with new emission standards. As a result, a number of old incinerators have closed down; some have been renovated and some new ones opened. Hence there been significant reductions in waste emissions. Electricity generation from waste combustion is now classified as power generation, hence the reported emission for waste incineration is even lower

PAH

Estimates for PHA emissions have been extensively revised. A full methodology and details of the estimates can be found in "Speciated PAH inventory for the UK, M Wenborn, P Coleman, NR Passant, E Lymberidi and RA Weir. AEA Technology 1998 AEAT-3512/REMC/20459131/ISSUE 1".

4 References

 IPCC, (1997), The Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories: The Reporting Instructions (Volume 1), The Workbook (Volume 2), The Reference Manual (Volume 3), ISBN 92-64-15578-3, IPCC WGI Technical Support Unit, Hadley Centre, Meteorological Office, Bracknell, UK.
Stewart, R, (1997), Gaseous and PM10 Emission Factors for Station W - a Modern CCGT Power Plant. AEA/20011002/002/Issue 1, National Environmental Technology Centre, Culham

UKOOA, (1997), Environmental Database for Emissions & Discharges from Offshore Installations, SCOPEC, Private Communication.