The report was produced by transport consultant Claire Holman for the NSCA's Cleaner Fuels Forum. The Forum's members include representatives of the oil and car industries, alternative fuel suppliers, retailers such as Tesco and Sainsbury's and environmental groups.
The report focuses on nitrogen dioxide and particulates, as air quality objectives for these pollutants will be particularly difficult to meet. Taking account of forthcoming EC Directives on fuel quality and vehicle emissions (see p 44 ), emissions of NOx and PM10 in urban areas are predicted to fall by 50% between 1995 and 2005. The Government says that reductions of 60% - or more at roadside locations - are needed to meet its air quality objectives for 2005 (ENDS Report 274, p 40 ).
However, the NSCA report concludes that cleaner fuels could make only a modest contribution to closing this 10% "policy gap". Even if all vehicles in urban areas used city diesel or low-benzene petrol, it says, emissions of PM10 and NOx would fall by only a further 2% and 3%, respectively.
The oil industry seized on the finding. Ian Upson, President of the UK Petroleum Industry Association, noted that "the production of large volumes of fuels meeting significantly changed fuels specifications would require substantial investment in our refineries, would take time and does not appear to be cost-effective." UKPIA's own studies have led it to claim that cleaner fuels might reduce road transport emissions of NOx and PM10 by as little as 1% by 2005, offering a "negligible impact" on air quality.
However, ENDS identified a serious error in the calculations which underpin the report's overall conclusions - and which, remarkably, was not picked up by members of the Forum who oversaw the work. Dr Holman then supplied ENDS with unpublished data - confirming that the correct figure for potential PM10 emission reduction is 8.4% (see table ).
On this basis, city diesel could plug much of the PM10 policy gap even if it did not completely displace conventional fuels in urban areas. Andrew Owens, Managing Director of city diesel supplier Greenergy, described the report as "a total stitch-up". As ENDS went to press, the Forum was about to hold a special meeting to discuss the implications of the finding.
Dr Holman's calculations were based largely on emission tests carried out by the oil and car industries in support of the European Commission's Auto/Oil programme. She concludes that city diesel can reduce PM10 emissions from light duty diesel vehicles by 20-30%. Fuel complying with the standard for 2000 agreed at EC level (ENDS Report 269, pp 43-44 ) would cut emissions by just 5%.
For heavy duty diesels, the Auto/Oil equations predict that city diesel will cut PM10 emissions by just 5-10%. But tests by London Transport - using an urban test cycle which is thought to be more realistic than the EC legislative cycle - found that city diesel cut PM10 emissions from buses by over 30%.
London Transport found that PM10 emissions fell by over 80% when a continuously regenerating particulate trap was also fitted. Such traps only operate effectively with low-sulphur diesel (ENDS Report 241, p 11 ). London Transport aims to run all of the capital's 5,500 buses on city diesel by the end of 1998, and by the end of March will have fitted traps or catalysts to 958 vehicles.
City diesel and low-benzene petrol offer a small 3-6% reduction in NOx emissions, the NSCA report concludes. But it adds that recent studies by the motor industry show that the low aromatic content of these reformulated fuels may lead to significantly greater NOx reductions than predicted by the Auto/Oil tests - a finding with important implications for the debate over the fuel quality Directive.
However, the report warns that the benefits of "near market" fuels such as compressed natural gas (CNG) and liquefied petroleum gas (LPG) "are not always as straightforward as is sometimes suggested." It offers a sneak preview of a study by the Energy Technology Support Unit, due to be published shortly. Gaseous fuels reduced PM10 emissions from all vehicles. But light duty vans using CNG and LPG can be worse than diesel on carbon dioxide, carbon monoxide and hydrocarbon emissions - while some buses running on gaseous fuels produced high NOx emissions.
The NSCA is urging the Government to increase the duty differential on cleaner conventional fuels so as to boost their uptake. The previous administration cut the duty on "ultra-low sulphur" diesel by 1p per litre - but the fuel remains more costly than conventional diesel (ENDS Report 262, pp 3-4 ). In February, the Treasury said that reducing the duty by a further 1p would cost about £5 million in 1998/99.
NSCA General Secretary Richard Mills argues that in the light of supply constraints, the maximum benefit from cleaner fuels can be obtained by targetting urban fleets. However, Sainsbury's already sells city diesel at 206 filling stations, where it accounts for 30% of total diesel sales - and over 50% in London where the firm charges the same price as ordinary diesel. Last year, Tesco also began selling city diesel at 50 sites in and around London. This summer, Sainsbury's plans to join Tesco in selling a reformulated "city petrol" in the capital.
Some of the major oil companies, including Shell, already supply limited quantities of city diesel to fleet operators - but are opposed to selling it on the forecourt. The revised findings of the NSCA report are a blow to the oil industry's bid to fend off demands that it produce greater quantities of cleaner fuels.
UKPIA's main remaining argument against reformulation is that removing sulphur would increase energy use in the refining process. But car manufacturers maintain that low-sulphur petrol is needed to pave the way for more fuel-efficient engines (ENDS Report 276, p 9 ). It is as yet unclear whether such a development would outweigh increases in CO2 emissions at the refinery.