I REFER to Mr W. M. Sulke's letter which appeared in the South China Morning Post, on February 4, headlined, ''Still heading in wrong direction''. He said that the proposed plan of the Environmental Protection Department (EPD) for tackling diesel emissions is wrong-headed. The EPD sees the most effective way to tackle diesel emissions is, firstly, in getting the small diesel vehicles to be replaced with petrol engined vehicles using unleaded petrol and catalytic converter technology. This would eliminate the black smoke and particle pollution caused by these vehicles, which now accounts for 60 to 70 per cent of health-threatening particulate emissions in some densely populated urban areas. Secondly, for larger vehicles, the strategy is to adopt the most stringent emissions standards which are being progressively introduced in Europe, together with bringing into Hong Kong the requisite associated cleaner fuels. Large vehicles contribute significantly towards territory-wide ambient particulate levels causing widespread violation of our health-based air quality standards. Mr Sulke raised two main contentions - one on emission from unleaded petrol vehicles as compared with diesel vehicle and the other on the quality of diesel fuel. Our vehicle emission professionals cannot agree with Mr Sulke that unleaded petrol vehicles with catalytic converters will increase pollution. A readily available, modern, unleaded petrol engine would emit no particulates and less of other pollutants than a comparable, but most advanced, diesel engine, which needs to feature multi-valves with catalytic converters, particle traps, turbo chargersand intercoolers, etc to attain low emissions. The only disadvantage of petrol engine is in its energy efficiency, but this must be balanced against the need to protect public health from the direct impact of diesel emissions at close range; we are not concerned just with overall ambient concentrations. We are not, incidentally, alone in holding our views. A report commissioned by the UK Department of the Environment has stated that the growing popularity of diesel cars is ''extremely bad for human health''. Regarding quality of local diesel fuel, we have always pointed out that it is not an issue for the existing fleet of diesel vehicles. Already at a low sulphur level, a further cut in the sulphur content of diesel fuel would only reduce the sulphates emitted but would achieve very little improvement on the mainly carbonaceous particulates emitted from existing engines. Further reduction in sulphur content is only necessary for the new generation of ''clean'' diesel engines which are coming into Hong Kong after April 1995, by which time 0.2 per cent sulphur diesel fuel will be made available. We are confident that we are heading in the right direction! RAYMOND LEUNG Ag Assistant Director (Air and Noise) Environmental Protection Department
