3 Nitrogen Dioxide

3.1 Pollutant concentration maps
Maps of estimated annual mean background NO₂ concentration have been calculated for 1996 and 2005. Full details of the methods used to calculate the 1996 map are given in Stedman (1998). A brief description of these methods is provided in Stedman, Bush and King (1998) along with a description of the methods used and assumption that have been made in order to project this map forward to provide estimates for 2005.

Maps for 1996 were calculated from a combination of a map of rural NO₂ concentration and estimates of low level NOx emissions on a 1 km square basis from the National Atmospheric Emissions Inventory (NAEI, Salway et al, 1997, Goodwin et al, 1997). The relationship between ambient annual mean NO₂ concentration and emission rates was calibrated using data from the DETR national monitoring networks (Broughton et al, 1998).

A map for 2005 was then calculated for comparison with the NAQS annual mean objective for NO₂ of 21 ppb. NO₂ is a secondary pollutant and is therefore not expected to respond in a simple linear fashion to the reductions in urban road traffic NO_x emissions that are expect to result from the implementation of current policies. A non-linear relationship between the reductions in NO_x emissions that are expected for this 'business as usual' scenario and the resulting ambient NO₂ concentrations was therefore adopted, as suggested by Derwent (pers comm).

3.2 Health benefits resulting from current policies
The estimated health benefits that are expected to result from the implementation of current national policy measures between 1996 and 2005 are listed in Table 3.1. The first column shows the number of admissions that has been calculated for the individual years for which maps have been calculated. The second column shows the cumulative reduction in hospital admissions calculated by adding up the marginal benefits between 1996 and 2005.

Table 3.1 Numbers of respiratory hospital admissions after predicted reductions in levels of NO₂ resulting from business as usual (UK Urban population).

Pollutant	Deaths Brought Forward		Emergency Respiratory Hospital Admissions (additional or brought forward)
NO2	In named year	Total reduction (from 1996 baseline)	In named year	Total reduction (from 1995 baseline)
1996	-		5160
2005	-	-	3505	8255
Notes Values have been rounded to the nearest 5. Hospital admission estimates are provided for NO2 as a sensitivity analysis (italics indicate the greater uncertainty for this pollutant, see EAHEAP, 1999).

3.3 Health benefits resulting from additional measures
The national modelling of NO₂ that has been carried out for the review of the NAQS (Stedman, Bush and King, 1998) has shown that the annual NO₂ objective is expected to be met at all background locations except inner London and at most roadside locations in 2005. Several alternative emissions reduction scenarios for NOx have been investigated within both national and local modelling studies in order to assess the impact of these measures on the policy gap between the concentrations of NO₂ at roadside and urban background locations which current policies are likely to deliver and the NAQS objective. The marginal health benefits that are expected to result from these additional reductions in emissions have also been calculated.

The alternative emissions reduction scenarios that have been examined are listed in Table 3.2. Marginal health benefits have been calculated for two scenarios for which emission reductions are targeted to London and are listed in Table 3.3. The cumulative total additional health benefits listed in Table 3.3 have been calculated on the basis of a linear additional reduction in admissions between 1996 and 2005. If measures were fully implemented at the start of 2005, rather than introduced gradually over the period between 1996 and 2005, then there would be no cumulative health benefits over this period relative to business as usual. The additional health benefits would be limited to those in 2005 and subsequent years.

Table 3.2 Alternative emissions reduction scenarios for 2005, relative to 2005 business as usual

scenario	emission reduction compared with business as usual
hl	30% less emissions from road traffic in inner London 10% less emissions from road traffic in outer London business as usual in the rest of the country
il	30% less emissions from cars in inner London 10% less emissions from cars in outer London business as usual in the rest of the country

Table 3.3. The impact of additional emissions reduction measures on additional and brought forward hospital admissions attributable to NO₂.

scenario	Marginal benefit in 2005	cumulative total benefit relative to business as usual
hl	62	310
il	19	95

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