Emissions factors for Euro III cars

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Comparison of current naei and new emission factors for Euro III and IV cars and petrol LGVs

This section discusses the new Euro III and IV emission factors for each pollutant in turn, comparing with existing factors used in the NAEI.

Nitrogen Oxides (NOx)

For petrol cars, the data are highly scattered especially at very low speeds and for medium-sized cars the data are scattered at all speeds. However, the tendency is for the Euro III factors to be below the current factors for Euro III in the NAEI at speeds above 40 kph.

Table 8 shows emission factors for petrol cars calculated from the new and current speed-emission factor relationships for Euro III and IV vehicles at typical average speeds on urban, rural and motorway roads and averaged over the fleet.

It was beyond the scope of this study to re-assess the emission factors for Euro II cars, but one of the main conclusions from a recent study by TRL on behalf of Netcen and Defra that gave a generalised review of all the vehicle emission factors used in the NAEI was that the NOx emission factor-speed equation for medium-sized Euro II petrol cars ought to be amended as new data examined by TRL suggested the current factors were too high, especially at high speeds (Boulter et al, 2005). We recommend that changing one of the coefficients in the emission factor-speed equation for Euro II medium-sized petrol cars originally developed by TRL would yield a curve consistent with the new recommendations of TRL and consistent with the relationships for small and large-sized Euro II petrol cars.

Table 8: NOx Emission factors for average petrol cars (in mg/km) on ULSP

mg NOx (as NO2)/km

Urban

Rural

Motorway

Current NAEI Euro II

195.2

209.3

316.2

Revised Euro II (see text below)

153.0

136.3

208.4

Current NAEI Euro III

85.4

91.5

138.3

New Euro III

65.6

43.0

67.4

Current NAEI Euro IV

61.0

65.4

98.7

Recommended Euro IV

53.6

34.5

53.2

       

Test data for 2 Euro IV vehicles sampled

     

<1.4l

12.7

13.5

15.9

>2l

79.0

52.3

10.2

The revised NOx emission factor-speed coefficients for Euro II medium-sized cars are given in Table 9 and the effect it has on fleet-averaged NOx factors for Euro II cars for different road types shown in Table 8.

Averaged over the fleet, the new Euro III emission factors are lower than the current NAEI factors for Euro III for all these road types.

Table 9: Revised NOx emission factor speed coefficients for Euro II medium-sized petrol cars and petrol LGVs

EF (g/km) = a + bv + cv2 + dv3 + e/v + f/v2 + g/v3 where v = average speed in kph

Pollutant

a

b

c

d

e

f

g

NOx

0.302

-0.0025

 

1.99E-07

 

 

 

Apart from at urban speeds, the new Euro III factors are also lower than the current NAEI factors for Euro IV petrol cars. At urban speeds they are similar. The recommended factors for Euro IV petrol cars for the fleet as a whole are slightly lower than the new factors for Euro III.

The data for the two Euro IV petrol cars that were tested tend to point towards the need to reduce the current NAEI factors for Euro IV petrol cars, although further data are required to confirm this.

Emission factors for Euro III and IV petrol LGVs are reduced from previous estimates reflecting reductions in the factors for medium sized petrol cars as shown in Table 10. Because factors for petrol LGVs are assumed to be the same as those for medium sized petrol cars, then the revision to the NOx factors for Euro II medium sized cars implies a revision to the Euro II factors for petrol LGVs. The revised emission factor-speed coefficients are given in Table 9 and the effect is has on NOx factors for Euro II LGVs for different road types shown in Table 10.

The data for diesel cars suggest the Euro III factors are slightly lower than values currently used in the NAEI at most speeds, although the differences between the current and new emission factors are smaller than they were for petrol cars.

Table 11 shows emission factors for average-sized diesel cars calculated from the new and current speed-emission factor relationships at typical average speeds on urban, rural and motorway roads.

Table 10: NOx Emission factors for average petrol LGVs (in mg/km) on ULSP

mg NOx (as NO2)/km

Urban

Rural

Motorway

Current NAEI Euro II

273

329

484

Revised Euro II (see text above)

181

171

250

Current NAEI Euro III

119

144

212

New Euro III

81

58

95

Current NAEI Euro IV

88

106

156

Recommended Euro IV

55

39

65

Table 11: NOx Emission factors for average diesel cars (in mg/km) on ULSD

mg NOx (as NO2)/km

Urban

Rural

Motorway

Current NAEI Euro II

547

505

815

Current NAEI Euro III

547

505

815

New Euro III

493

453

647

Current NAEI Euro IV

273

253

407

Recommended Euro IV

226

207

296

Averaged over the fleet, the new Euro III emission factors are lower than the current NAEI factors for Euro III for all these road types.

The new Euro III factors for diesel cars remain higher than the existing values used for Euro IV diesel cars in the NAEI. The method for estimating emission factor-speed equations for Euro IV cars leads to a lower estimate of emission factors for Euro IV diesel cars than had previously been estimated.

Particulate Matter (PM)

For petrol cars, the emission factors for PM are low and highly scattered. This is probably a consequence of the PM deposits approaching the resolution of the PM measurement technique. The statistical fits to the data tend to show the Euro III factors to be higher then the current factors for Euro III in the NAEI at low speeds, but lower than the current NAEI factors at high speeds. Recent research on the repeatability of the current PM measurement techniques suggest that PM measurement at these levels are strongly influenced by the dilution air background particle concentrations. This can lead to a systematic increase in the PM levels measured and the factors implied by the data should be regarded as upper limits in the actual PM emission factors for petrol cars.

PM emissions from petrol cars are not regulated and the current NAEI, in the absence of any other information to go by, assumes that PM emission factors for Euro III and IV petrol cars are the same as their Euro II counterparts for which the current factors used are based on the TRL (2001) report. Euro III petrol cars make a very small contribution to the total PM inventory for road transport (<1% in mass terms) so the high scatter and uncertainty in the PM factors do not bear any great significance.

Table 12 shows emission factors for average-sized petrol cars calculated from the new and current speed-emission factor relationships at typical average speeds on urban, rural and motorway roads.

Averaged over the fleet, the new Euro III emission factors are higher than the current NAEI factors for Euro III for urban road types, but lower for motorway road types.

Table 12: PM Emission factors for average petrol cars (in mg/km) on ULSP

mg PM/km

Urban

Rural

Motorway

Current NAEI Euro II

0.8

1.4

5.4

Current NAEI Euro III

0.8

1.4

5.4

New Euro III

1.5

1.6

2.2

Current NAEI Euro IV

0.8

1.4

5.4

Recommended Euro IV

1.5

1.6

2.2

       

Test data for 2 Euro IV vehicles sampled

     

<1.4l

0.8

0.5

1.1

>2l

1.2

1.1

3.1

As there are no limit values on PM set for Euro IV petrol cars, we recommend using the new Euro III factors for PM for these vehicles. The data for the two Euro IV petrol cars that were tested suggest the factors are lower than these at urban and rural speeds, but are similar at higher speeds.

Emission factors for Euro III and IV petrol LGVs are changed from previous estimates reflecting reductions in the factors for medium sized petrol cars, as shown in Table 13

These vehicles make a very small contribution to total road transport PM emissions in the inventory.

Table 13 PM Emission factors for average petrol LGVs (in mg/km) on ULSP

mg PM/km

Urban

Rural

Motorway

Current NAEI Euro II

0.9

1.3

4.8

Current NAEI Euro III

0.9

1.3

4.8

New Euro III

2.1

2.1

2.1

Current NAEI Euro IV

0.9

1.3

4.8

Recommended Euro IV

2.1

2.1

2.1

The data for diesel cars suggest the Euro III factors are slightly higher than values currently used in the NAEI at most speeds.

Table 14 shows emission factors for average-sized diesel cars calculated from the new and current speed-emission factor relationships at typical average speeds on urban, rural and motorway roads.

Table 14 PM Emission factors for average diesel cars (in mg/km) on ULSD

mg PM/km

Urban

Rural

Motorway

Current NAEI Euro II

51.4

37.3

58.3

Current NAEI Euro III

31.5

22.9

35.8

New Euro III

35.2

30.5

45.7

Current NAEI Euro IV

16.6

12.0

18.8

Recommended Euro IV

19.3

16.6

25.6

Averaged over the fleet, the new Euro III emission factors are similar to the current NAEI factors for Euro III at urban speeds, but are higher at speeds on rural and highway roads.

The new Euro III factors for diesel cars remain higher than the existing values used for Euro IV diesel cars in the NAEI. The method for estimating emission factor-speed equations for Euro IV cars leads to a higher estimate of emission factors for Euro IV diesel cars than had previously been estimated.

In addition to the diesel vehicles discussed above, the NAEI calculates separately the PM emissions from passenger cars fitted with diesel particulate filters (DPF). The assumption used is that the effect of the DPF is to reduce PM emissions by 90%. This assumption was reviewed in this project. One of the vehicles tested had a DPF (the Peugeot 406 FAP). This vehicle meets Euro III emission standards and has a 2.2 litre engine. Its speed related PM emission function is "U" shaped, i.e. follows that of the other Euro III vehicles being higher for the slower and faster drive cycles. The average emission factor for PM for all nine drive cycles was 4.4 µg/km, whereas for the other Euro III diesels > 2.0 litres the equivalent average is 54.4 µg/km. Hence for this single example its PM emissions are 8.1% of that from equivalent vehicles not fitted with a DPF, implying a 92% reduction in PM emissions due to the DPF.

However, as noted above when considering the PM emissions from petrol fuelled vehicles, the current PM measurement technique is strongly influenced by dilution air background particle concentrations. This potentially leads to a systematic increase in the PM levels measured and would mean the efficiency of the DPF exceeds the 92% implied by this vehicle. On balance, it is felt a vehicle sample of one is insufficient to be the basis for revising the PM emission factors for diesel vehicles fitted with a trap. Notwithstanding, despite uncertainties regarding how representative the Peugeot data is, it does support the approach adopted within the NAEI. Further, if the reduction in PM emissions is greater than 90%, the impact of this within the NAEI would be minimal.

Carbon Monoxide (CO)

The data for CO show a high degree of scattering. For petrol cars, the Euro III factors are lower than current factors used in the NAEI for small cars (except at the highest speeds), very similar to current factors for medium-sized cars and higher for larger cars.

Table 15 shows emission factors for average-sized petrol cars calculated from the new and current speed-emission factor relationships at typical average speeds on urban, rural and motorway roads.

Table 15 CO Emission factors for average petrol cars (in mg/km) on ULSP

mg CO/km

Urban

Rural

Motorway

Current NAEI Euro II

684

493

411

Current NAEI Euro III

637

459

383

New Euro III

420

395

516

Current NAEI Euro IV

506

364

304

Recommended Euro IV

420

395

516

       

Test data for 2 Euro IV vehicles sampled

     

<1.4l

40

81

183

>2l

104

78

159

Averaged over the fleet, the new Euro III emission factors are lower than the current NAEI factors for Euro III on urban and rural roads, but higher on motorway roads.

The new CO factors imply Euro III petrol cars are below CO limits for Euro IV, so emission factor speed equations for Euro IV are assumed to be the same as for Euro III cars. This leads to fleet-averaged CO emission factors for Euro IV petrol cars being lower than current estimates for Euro IV at urban speeds, but higher at motorway and rural speeds.

The data for the two Euro IV petrol cars that were tested are significantly lower and point towards the need to reduce the current NAEI factors for Euro IV petrol cars. Further data are required to confirm this.

Revised CO emission factors for Euro III and IV petrol LGVs calculated from the emission factor speed equations are given in Table 16. Emission factor speed equations for Euro IV are assumed to be the same as for Euro III vehicles.

Table 16: CO Emission factors for average petrol LGVs (in mg/km) on ULSP

mg CO/km

Urban

Rural

Motorway

Current NAEI Euro II

477

418

394

Current NAEI Euro III

444

389

367

New Euro III

473

394

406

Current NAEI Euro IV

353

309

292

Recommended Euro IV

473

394

406

The data for diesel cars suggest the Euro III factors are significantly lower than values currently used in the NAEI at most speeds for small cars, although they are fairly similar for large diesel cars.

Table 17 shows emission factors for average-sized diesel cars calculated from the new and current speed-emission factor relationships at typical average speeds on urban, rural and motorway roads.

Table 17 CO Emission factors for average diesel cars (in mg/km) on ULSD

mg CO/km

Urban

Rural

Motorway

Current NAEI Euro II

247

76

76

Current NAEI Euro III

148

46

46

New Euro III

38

27

24

Current NAEI Euro IV

148

46

46

Recommended Euro IV

38

27

24

Averaged over the fleet, the new Euro III emission factors are lower than the current NAEI factors for Euro III for all these road types.

The new CO factors imply Euro III diesel cars are below CO limits for Euro IV, so emission factor speed equations for Euro IV are assumed to be the same as for Euro III cars. This leads to fleet-averaged CO emission factors for Euro IV diesel cars being lower than current estimates for Euro IV at all speeds.

Total Hydrocarbons (THC)

The data for THC show a high degree of scattering. For petrol cars, the Euro III factors tend to be lower than current factors used in the NAEI for small and medium-sized cars and are similar for large cars

Table 18 shows emission factors for average-sized petrol cars calculated from the new and current speed-emission factor relationships at typical average speeds on urban, rural and motorway roads.

Table 18 THC Emission factors for average petrol cars (in mg/km) on ULSP

mg THC/km

Urban

Rural

Motorway

Current NAEI Euro II

39.1

27.3

28.4

Current NAEI Euro III

30.1

21.0

21.9

New Euro III

17.7

12.0

16.9

Current NAEI Euro IV

29.0

20.3

21.1

Recommended Euro IV

17.7

12.0

16.9

       

Test data for 2 Euro IV vehicles sampled

     

<1.4l

5.8

4.6

10.5

>2l

6.1

2.4

19.2

Averaged over the fleet, the new Euro III emission factors are lower than the current NAEI factors for Euro III for all these road types.

The new THC factors imply Euro III petrol cars are below THC limits for Euro IV, so emission factor speed equations for Euro IV are assumed to be the same as for Euro III cars. This leads to fleet-averaged THC emission factors for Euro IV petrol cars being lower than current estimates for Euro IV at all speeds.

The data for the two Euro IV petrol cars that were tested are significantly lower and point towards the need to reduce the current NAEI factors for Euro IV petrol cars. Further data are required to confirm this.

Revised THC emission factors for Euro III and IV petrol LGVs calculated from the emission factor speed equations are given in Table 19. Emission factor speed equations for Euro IV are assumed to be the same as for Euro III vehicles.

Table 19 THC Emission factors for average petrol LGVs (in mg/km) on ULSP

mg THC/km

Urban

Rural

Motorway

Current NAEI Euro II

34.4

31.1

30.4

Current NAEI Euro III

26.5

24.0

23.4

New Euro III

10.6

7.2

9.3

Current NAEI Euro IV

25.5

23.1

22.6

Recommended Euro IV

10.6

7.2

9.3

The data for diesel cars suggest the Euro III factors are lower than values currently used in the NAEI at most speeds.

Table 20 shows emission factors for average-sized diesel cars calculated from the new and current speed-emission factor relationships at typical average speeds on urban, rural and motorway roads.

Averaged over the fleet, the new Euro III emission factors are lower than the current NAEI factors for Euro III for all these road types.

The new THC factors imply Euro III diesel cars are below THC limits for Euro IV, so emission factor speed equations for Euro IV are assumed to be the same as for Euro III cars. This leads to fleet-averaged THC emission factors for Euro IV diesel cars being lower than current estimates for Euro IV at all speeds.

Table 20 THC Emission factors for average diesel cars (in mg/km) on ULSD

mg THC/km

Urban

Rural

Motorway

Current NAEI Euro II

62.8

31.0

25.4

Current NAEI Euro III

43.9

21.7

17.8

New Euro III

19.4

12.6

8.6

Current NAEI Euro IV

40.2

19.8

16.3

Recommended Euro IV

19.4

12.6

8.6

Carbon Dioxide (CO2)

The Euro III data for CO2 are less scattered than for the other pollutants. The curves show the usual asymmetric 'U'-shape, but are more flattened off than the curves for Euro II at the higher speed range, appearing more 'L'-shaped in nature.

For petrol cars, the Euro III factors for CO2 from the sample tested tend to be lower than the current factors used in the NAEI. This is also reflected by the fact that the fleet-weighted average CO2 factor derived from the best-fit emission functions at the speed of the NEDC Combined Cycle is 163 g/km compared with the DfT/SMMT average value (forming the basis of the current NAEI factor) of 178 g/km for a Euro III petrol car.

Table 21 shows emission factors for average-sized petrol cars calculated from the new and current speed-emission factor relationships at typical average speeds on urban, rural and motorway roads. The new factors for Euro III and IV cars are from equations based on the shape of the speed curves exhibited by the new test data for Euro III cars, re-scaled to fit the DfT/SMMT average factors for Euro III and IV petrol cars.

Table 21 CO2 Emission factors for average petrol cars (in g/km) on ULSP

g CO2/km

Urban

Rural

Motorway

Current NAEI Euro II

180

171

206

Current NAEI Euro III

169

160

194

New Euro III (re-scaled)

167

150

161

Current NAEI Euro IV

151

143

173

Recommended Euro IV

149

134

144

       

Test data for 2 Euro IV vehicles sampled

     

<1.4l

124

109

129

>2l

161

135

150

The main difference between the new and current factors for Euro III and IV cars is the significant reduction in emissions at high speeds reflecting the flattening off in the shape of the speed-emission curve at high speeds.

The data for the two Euro IV petrol cars that were tested show low emission levels consistent with the recommended Euro IV factors.

It should be noted that in accordance with internationally agreed emission reporting protocols (e.g. IPCC), the NAEI calculates emissions of CO2 from the road transport sector from a top-down approach based on national fuel sales rather than a bottom-up method based on emission factors and traffic data that are used for other pollutants. Therefore, any changes to the CO2 factors for road vehicles would not affect the UK's inventory on CO2, but it would affect how the fuels are allocated between different vehicle types. In addition, changes in CO2 emission factors could affect the results of CO2 emissions modelling on a more local scale.

The new CO2 emission factors calculated for Euro I-IV petrol LGVs for urban, rural and motorway roads are shown in Table 22.

Table 22: CO2 Emission factors for average petrol LGVs (in g/km) on ULSP

g CO2/km

Urban

Rural

Motorway

Euro I

250

223

294

Euro II

248

221

291

Euro III

240

214

282

Euro IV

228

203

268

For diesel cars, the Euro III factors for CO2 from the sample tested are lower than the current factors used in the NAEI. This is also reflected by the fact that the fleet-weighted average CO2 factor derived from the best-fit emission functions at the speed of the NECD Combined Cycle is 134 g/km compared with the DfT/SMMT average value (forming the basis of the current NAEI factor) of 164 g/km for a Euro III diesel car.

Table 23 shows emission factors for average-sized diesel cars calculated from the new and current speed-emission factor relationships at typical average speeds on urban, rural and motorway roads. Again, the new factors for Euro III and IV cars are from equations based on the shape of the speed curves exhibited by the new test data for Euro III cars, re-scaled to fit the DfT/SMMT average factors for Euro III and IV diesel cars.

Table 23 CO2 Emission factors for average diesel cars (in g/km) on ULSD

g CO2/km

Urban

Rural

Motorway

Current NAEI Euro II

171

157

208

Current NAEI Euro III

153

140

186

New Euro III

154

144

165

Current NAEI Euro IV

139

127

169

Recommended Euro IV

140

131

150

Again, the main difference between the new and current factors for Euro III and IV cars occurs at high speeds.

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