6 Alternative emissions scenarios

6.1 National traffic emission reduction measures

Roadside NO2 concentrations have also been estimated for several alternative emission reduction scenarios in order to examine the impact of additional reductions in NOx emissions from traffic on the likely extent of exceedance of the annual mean objective and limit value for NO2. We have estimated the roadside NO2 that would be likely to result from two national emissions reduction scenarios and two scenarios for which emission reductions are targeted to London(DETR).

Tables 6.1 and 6.2 show the NOx emission reduction factors for the two national emission reduction scenarios that we have examined (Murrells pers comm). The 30% reductions are relative to the 2005 (or 2009) business as usual emissions.

Table 6.1. Urban road traffic NOx national emissions reduction scenarios, factors relative to 1996.

	scenario	2005	2009
Business as usual	a	0.44	0.33
30% less emissions from traffic	h	0.31	0.23
30 % less emissions from cars (other traffic as business as usual)	i	0.37	0.29

Table 6.2. Background NO_x national emissions reduction scenarios, factors relative to 1996.

	scenario	2005	2009
Business as usual	a	0.50	0.40
30% less emissions from traffic	h	0.38	0.31
30 % less emissions from cars (other traffic as business as usual)	i	0.44	0.36

Tables 6.3 and 6.4, below, show the number of major road links with estimated concentrations greater than 21 ppb for these two scenarios along with the number of links for business as usual. We have estimated concentrations for a total of 7508 urban road links, of which 705 are in Inner London and 785 are in Outer London.

It is clear that the number of road links with concentrations above the annual mean objective is significantly reduced for these scenarios. It is likely, however, that many of the links with high concentrations in cities other than London may not have housing at the roadside and concentrations do not need to be less than 21 ppb for this links. This is discussed further in section 7.

Table 6.3. Number of built up major road links with estimated annual mean concentrations greater than 21 ppb in 2005.

scenario	UK	Inner London	Outer London	Other cities
a	761	395	100	266
h	116	66	13	37
i	360	206	40	114

Table 6.4. Number of built up major road links with estimated annual mean concentrations greater than 21 ppb in 2009.

scenario	UK	Inner London	Outer London	Other cities
a	170	102	19	49
h	21	13	4	4
i	87	54	10	23

Traffic emission reduction measures in London

We have also estimated the roadside NO2 concentrations that would be likely to result from two scenarios (hl and il) in which additional emission reductions are targeted to London.

Tables 6.5 and 6.6 show the NOx emission reduction factors for the two London emission reduction scenarios that we have examined (Murrells pers comm). Scenario hl has a 30% reduction in traffic emissions in inner London and a 10% reduction in outer London. Scenario il has a 30% reduction in emissions from cars in inner London and a 10% reduction in outer London. NOx emissions in the rest of the UK are assumed to be the same as the business as usual scenario.

Table 6.5. Urban road traffic NOx London emissions reduction scenarios, factors relative to 1996.

	scenario	Inner London		Outer London
		2005	2009	2005	2009
Business as usual	a	0.44	0.33	0.44	0.33
30%/10% less emissions from traffic	hl	0.31	0.23	0.40	0.30
30%/10% less emissions from cars (other traffic as business as usual)	il	0.37	0.29	0.42	0.32

Table 6.6. Background NOx London emissions reduction scenarios, factors relative to 1996.

	scenario	Inner London		Outer London
		2005	2009	2005	2009
Business as usual	a	0.50	0.40	0.50	0.40
30%/10% less emissions from traffic	hl	0.38	0.31	0.46	0.37
30%/10% less emissions from cars (other traffic as business as usual)	il	0.44	0.36	0.48	0.39

Tables 6.7 and 6.8 show the number of major road links with estimated concentrations greater than 21 ppb for these two scenarios along with the number of links for business as usual. The numbers of links with concentrations greater than 21 ppb is obviously the same as the business as usual scenario for all road links outside London.

Maps of annual mean background NO2 concentrations for 2005 and 2009 can also be calculated for these two scenarios.

Table 6.7. Number of built up major road links with estimated annual mean concentrations greater than 21 ppb in 2005.

scenario	UK	Inner London	Outer London	Other cities
a	761	395	100	266
hl	388	66	56	266
il	549	206	77	266

Table 6.8. Number of built up major road links with estimated annual mean concentrations greater than 21 ppb in 2009.

scenario	UK	Inner London	Outer London	Other cities
a	170	102	19	49
hl	74	13	12	49
il	118	54	15	49

Predicted NO2 concentrations for individual roadside monitoring sites for the alternative emissions reductions scenarios are listed in Table 6.9. Estimated concentrations for 1997 and predicted concentrations for the business as usual scenario are shown in Table 5.1