The 1997 National Air Quality Strategy (NAQS) included the following specific objectives for benzene and 1,3-butadiene, to be achieved by the end of 2005:

benzene: 5 ppb, measured as a running annual mean

1,3-butadiene: 1 ppb, measured as a running annual mean

The recently completed review of the NAQS included a proposal to bring the date for achievement of these objectives forward to the end of 2003.

The Commission of the European Communities has published a proposal for a Directive in relation to limit values for benzene and carbon monoxide. This is the second Daughter Directive to be brought forward by the European Commission under the Framework Directive on Ambient Air Quality Assessment and Management. The proposed limit value for benzene is 5 m gm^-3 (1.542 ppb), as an annual mean, to be achieved by 1 January 2010.

The projections of roadside benzene and 1,3-butadiene that have been published in the review of the NAQS (DETR et al, 1999, Stedman and Dore, 1998) and for comparison with the EU Daughter Directive limit value (Stedman, 1999) were based on emissions projections derived from the 1996 National Atmospheric Emissions Inventory (NAEI) road transport model. Emissions projections based on the 1997 NAEI road transport model are now available and estimates of roadside concentrations have been re-calculated using these revised projections.

The estimates of concentrations of benzene and 1,3-butadiene calculated on the basis of the 1996 NAEI indicate that current national policies are likely to be sufficient to reduce roadside concentrations to below the objectives for the end of 2003 proposed in the review of the NAQS (DETR et al, 1999). No road links were predicted to have benzene concentrations higher than the objective in 2003 and only one road link was predicted to have a roadside 1,3-butadiene concentration higher than the objective in 2003. The projections calculated here, based on the 1997 NAEI road transport model, confirm this conclusion.

Projections based on the 1996 NAEI indicate that very few road links are expected to have concentrations higher than the proposed EU limit value of 5 m gm^-3 by the end of 2006 and very few are expected to have concentrations greater than 5 m gm^-3 with a 20% safety margin by the end of 2008. A total of 12 road links are projected to have an annual mean benzene concentration in excess of 5 m gm^-3 in 2009 for the predictions based on the 1997 NAEI, and a total of 75 road links are expected to have concentrations greater than 5 m gm^-3 with a 20% safety margin. The majority of the road links with the highest estimated benzene concentrations are in inner London and are also expected to be at risk of exceeding the proposed EU limit value for annual mean NO₂.

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