National Atmospheric Emissions Inventory

Appendix 1

The Methodology of the National Atmospheric Emissions Inventory

2.9 Other Transport

 2.9.1 Air Transport

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, 1997b) and emission factors calculated as the emission of pollutant per aircraft movement. The aircraft emission factors are shown in Table A25 and are for a large airport (Heathrow) and a smaller airport (Gatwick). In the calculations the smaller airport factors are used for the other British Airports.

The emission factors were derived from studies at Heathrow and Gatwick airports discussed by Munday (1990) and Leech (1991) . The following information was used:


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


From the time spent in each stage it was possible to estimate the fuel consumed and hence the emission of pollutant. The SO2 emission factor is corrected for the year to year variation in the sulphur content of aviation fuel. 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.

Table A25 Aircraft Emission Factors (kg/movement)

  CO2 1 CH4 3 NOx CO NMVOC3 SO22 BS
Large Airport 797 0.422 15.7 12.4 3.97 2.17 0.899
Smaller Airport 401 0.212 7.88 6.22 2.00 1.09 0.452
1 Emission factor as kg carbon/ aircraft movement
2 1996 value based on Institute of Petroleum (1997)
3 Based on total hydrocarbon emission. Assumes methane is 9.6% (EMEP/CORINAIR, 1996)

2.9.2 Shipping

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. The emissions from Fishing and Coastal Shipping are estimated according to the base combustion module using emission factors given in Table A3 and fuel consumption data from DTI (1997).

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. The revisions to the Offshore Oil and Gas emissions have removed the small double counts that existed in previous inventories.

2.9.3 Military Emissions

Emissions were estimated from:


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(1997a). Naval fuel consumption was supplied by MOD(1997). The emission factors used are shown in Table A26. The emission factors used for military aircraft are cruise factors appropriate to domestic jets, so estimates will be approximate.

Table A26 Emission Factors Used for Military Emissions

  CO21 CH4 N2O NOx CO NMVOC SO2 BS PM10
Air 859a 0.0825b 0.1d 23.7e 4e 0.667b 0.8f 0.98g NE
Naval 857a 0.288c 0.2e 57e 7.4e 2.11b 19.4e 1.35g 1.07
  1 CO2 as carbon
  a UKPIA(1989)
  b UNECE/CORINAIR(1996) based on total hydrocarbon emission factor
  and speciation data
  c UNECE/CORINAIR(1996) based on total hydrocarbon emission factor
    and speciation data from IPCC(1997)
  d IPCC(1997)
  e UNECE/CORINAIR(1996)
  f Institute of Petroleum (1997)
  g EMEP (1990)

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.

2.9.4 Other Off-Road Sources

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 combines; 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:


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:

  Ej = Nj . Hj . Pj . Lj . (1 - Yj . aj ). ej
where
Ej = Emission of pollutant from class j (kg/year)
Nj = Population of class j.
Hj = Annual usage of class j (h/year)
Pj = Average power rating of class j (kW)
Lj = Load factor of class j (-)
Yj = Average age of class j (years)
aj = Age factor of class j (y-1)
ej = Emission factor of class j (kg/kWh)

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

  Evj = Nj . Hj . evj
where
Evj = Evaporative emission from class j (kg)
evj = Evaporative emission factor for class j (kg/h)

Population and age data were supplied by a market research telephone poll amongst equipment suppliers and trade associations by Precision Research International on behalf of DOE. (PRI, 1995). The annual usage data was 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 (1993). The load factors were taken from Samaras(1996).

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:

  1. Aggregate emission factors were calculated for each of the four main categories listed above as
      ep = E
       F
    where
      ep = Aggregate emission factor for main .
          NAEI category (kg/t fuel)
      E = Sum of emissions of pollutant from classes within
          main NAEI category calculated from the
          population approach (kg)
      F = Sum of fuel consumption from classes within
          main NAEI category calculated from the population
          approach (tonnes)
  2. Estimates were derived for the fuel consumptions for the years 1970-1995 for each of the four main categories

  3. The emission for each of the four main NAEI categories was estimated as:
      Ep = ep . Ap
    where
      Ap = Fuel consumption of NAEI main category p (tonnes)
    Emissions from off-road sources are particularly uncertain. The aggregate emission factors calculated for each NAEI category are shown in Table A27. 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)

    Table A27 Aggregate Emission Factors for Off-Road Source Categories (t/kt fuel)

    Source Fuel Ca CH4 N2O NOx CO NMVOC SO2b BSc PM10
    Domestic House&Garden DERV 857 0.159 1.3 53.5 26.6 12.1 1.8 18 1.21
    Domestic House&Garden Petrol 855 6.84 0.0279 2.90 1382 626 0.73 0.645 1.006
    Agricultural Power Units Gas Oil 857 0.163 1.31 54.0 16.8 7.56 2.8 18 1.07
    Agricultural Power Units Petrol 855 7.53 1.31 1.98 1367 753 0.518 0.645 1.006
    Industrial Off-road Gas Oil 857 0.165 1.37 50.5 13.6 6.05 2.8 18 1.07
    Industrial Off-road Petrol 855 4.89 0.0726 9.08 1965 98.6 0.518 0.645 1.006
    Aircraft Support Gas Oil 857 0.164 1.37 56.5 12.4 5.49 2.8 18 1.07
      a Emission factor as kg carbon/t. UKPIA (1989)
      b Institution of Petroleum, (1997),
      c Keddie et al. (1978), Timmis et al. (1988)