The NAEI category Air Transport gives an estimate of emissions within a 1000 m ceiling of takeoff and landing. This represents, roughly the boundary layer and emissions into it.

The estimates are calculated from the number of aircraft movements at British airports (DETR, 2000b) and emission factors calculated as the emission of pollutant per aircraft movement. It is however more usual to express emission factors as the emission per landing and takeoff cycle.

For an aircraft landing and takeoff cycle (LTO) the following stages of operation are considered:

• approach from 1000m
• taxi
• takeoff
• climb out to 1000m.

UK aircraft statistics are reported as aircraft movements (i.e. takeoff or landings) and so the emission factors are reported as emission per movement. It follows that one LTO is equal to two aircraft movements.

The aircraft emission factors used are taken from LRC (1998) and are derived from the Local Inventory studies at Heathrow, Gatwick, Birmingham, Manchester, London City, Southampton, Liverpool, Bristol and Coventry. Detailed data on all UK airports was available for 1996 - 1998. Each airport was allocated a set of emission factors taken from those listed. Where an airport was not include in the study, factors from an airport of similar size were used. Thus from the aircraft movement data and local emission factor data it was possible to calculate total UK emissions. For the years where detailed airport data were not available, estimates were based on emission factors for Heathrow, Gatwick and an aggregate of all other airports (Rest). The aggregate factors are shown in Table A35

Table A35 Aircraft Emission Factors for 1999 (kg/movement)

1 Emission factor as kg carbon/ aircraft movement

2. 1999 value based on UKPIA (2000)
3. Estimated from total hydrocarbon factor corrected using IPCC(1997) methane factor

Emissions of methane and nitrous oxide were calculated using IPCC(1997) emission factors which are quoted for domestic and international flights. They are shown in Table A36.

Table A36 Aircraft Emission Factors for Methane and Nitrous Oxide (kg/movement)

The NAEI estimates emissions from Fishing and Coastal shipping. The old category Other UK Shipping which reported emissions from international shipping within UK coastal waters is no longer used following the changeover to the UNECE/CORINAIR SNAP 94 system. This has been replaced by the category International Marine. The emissions from Fishing, Coastal Shipping and International Marine are estimated according to the base combustion module using emission factors given in Table A3 and fuel consumption data from DTI (2000). Emissions from International Marine are based on the Marine Bunkers fuel consumption reported in DTI (2000) corrected for naval consumption. Emissions are not included in the National Total.

The coastal shipping category does contain emissions from offshore fuel use. A proportion of this will be marine transport associated with the offshore industry but some is fuel oil use in turbines, motors and heaters on offshore installations.

Emissions were estimated from:

• military aircraft
• naval vessels

based on estimates of their fuel consumption. Aircraft fuel consumption is given in ONS(1995) up to 1992, however, this data is no longer collected and reported and for subsequent years data is obtained directly from MOD(2000a). Naval fuel consumption was supplied by MOD(2000). The emission factors used are shown in Table A3. The aviation fuel data contains fuel used overseas. Takeoff and landing data for military aircraft are not available so the estimates are based on fuel consumption data and cruise emission factors for small jet aircraft, so estimates will be approximate.

These cover emissions from a range of portable or mobile equipment powered by reciprocating diesel or petrol driven engines. They include agricultural equipment such as tractors and combine harvesters; construction equipment such as bulldozers and excavators; domestic lawn mowers; aircraft support equipment; and industrial machines such as portable generators and compressors. In the Inventory they are grouped into four main categories:

• domestic house&garden
• agricultural power units (includes forestry)
• industrial offroad (includes construction and quarrying)
• aircraft support.

The estimates are calculated using a modification of the methodology given in EMEP/CORINAIR(1996). This involves the estimation of emissions from around seventy classes of off-road source using the following equation for each class:

E_j = N_j . H_j . P_j . L_j . (1 - Y_j . a_j /2). e_j

where

E_j = Emission of pollutant from class j (kg/year)

N_j = Population of class j.

H_j = Annual usage of class j (h/year)

P_j = Average power rating of class j (kW)

L_j = Load factor of class j (-)

Y_j = Average age of class j (years)

a_j = Age factor of class j (y^-1)

e_j = Emission factor of class j (kg/kWh)

For petrol engined sources, evaporative NMVOC emissions are also estimated as:

E_vj = N_j . H_j . e_vj

where

E_vj = Evaporative emission from class j (kg)

e_vj = Evaporative emission factor for class j (kg/h)

The population and machinery lifetime data have been revised based on a new DETR sponsored survey of machinery sales and lifetime by Off-Highway Research Ltd (2000). These data have been used to revise or supplement the previous activity data sets. These were market research telephone polls amongst equipment suppliers and trade associations by Precision Research International on behalf of DOE. (PRI, 1995, 1998). The annual usage data were taken either from the PRI poll or published data (Samaras et al, 1993,1994). The emission factors used came mostly from EMEP/CORINAIR (1996) though a few of the more obscure classes were taken from Samaras et al (1993). The load factors were taken from Samaras (1996).

Generally the OHRL data was used to revise the PRI population/lifetime data for sources other than balers, combines, agricultural mowers, agricultural tractors, off-road trucks, fork lifts, generators, cement mixers and lawnmowers where the PRI studies had placed particular effort.

It was possible to calculate fuel consumptions for each class based on fuel consumption factors given in EMEP/CORINAIR (1996). Comparison with known fuel consumption for certain groups of classes (e.g. agriculture and construction) suggested that the population method over estimated fuel consumption by factors of 2-3. Hence the methodology was modified in the following way:

Emissions from off-road sources are particularly uncertain. The revisions in the population data produced higher fuel consumption estimates. The petrol consumption increased markedly but is still only a tiny proportion of total petrol sales. The aggregate emission factors calculated for each NAEI category are shown in Table A37. The emission factors used for carbon dioxide and sulphur dioxide were the standard emission factors for DERV, gas oil and petrol given in Table A3. The black smoke emission factors were the default factors for petrol and diesel engines given in Table A3 (Keddie et al., 1978; Timmis et al., 1988)

a Emission factors for 1999

b Emission factor as kg carbon/t. UKPIA (1989)

c UKPIA (2000),

d Keddie et al. (1978), Timmis et al. (1988)

e Factor based on 50cc , 2 stroke moped engine - see Section 2.9.3

The NAEI reports emissions from both stationary and mobile sources. The source, railways (stationary) reports emissions from the combustion of burning oil, fuel oil and natural gas by the railway sector. The natural gas emission derives from generation plant used for the London Underground. These stationary emissions are reported under 02 Commercial &Institutional in the UNECE reporting system. Most of the electricity used by the railways for electric traction is supplied from the public distribution system, so the emissions arising from its generation are reported under 01 Public Power. These emissions are based on fuel consumption data from DTI (2000). Emission factors are reported in Tables A3 and A6.

The NAEI reports emissions from diesel trains as railways (freight), railways (intercity) and railways (regional). These estimates are based on the gas oil consumption for railways reported in DTI (2000). Emissions from diesel trains are reported under 08 Other Transport and Mobile Machinery.

Diesel train journeys have been split into three categories: freight, intercity and regional. Carbon dioxide, sulphur dioxide and N₂O emissions are calculated based on fuel based emission factors using fuel consumption data from DTI (2000). This fuel consumption is distributed according to railway km data from DETR (1996c) on the three types of journey ; an assumed mix of locomotives for each journey type; and fuel consumption factors for the different types of locomotive (LRC, 1998). The detailed railway km data is only available up to 1995 and later years are interpolated using 1995 data. Emissions of CO, NMVOC, NO_x , PM₁₀ and methane are based on the railway km estimates and emission factors for the various types of locomotive used. The emission factors shown in Table A38 are aggregate factors so that all factors are reported on the common basis of fuel consumption.

Table A38: Railway Emission Factors (kt/Mt)