Magic diesel

I refer to the backpage article "Edible Oil producing bio-diesel" (June 5). Many virtues were ascribed to bio-diesel, unfortunately in a manner that made it difficult to decide whether these came from Pippo Psaila or the reporter. In any case, some of them were echoed by Minister Francis Zammit Dimech in his ministerial offering for World Environment Day.

The statements about emissions were very inaccurate. Bio-diesel does not contain sulphur; mineral diesel is now down to 0.05 per cent sulphur even in these islands, according to Enemalta. Such a sulphur content makes diesel an insignificant source of SO2; by far the largest sources are the two power stations. In any case sulphur is not carcinogenic as claimed in the article, at least according to reputable (as against barefoot) epidemiologists. It is an irritant of the mucous membranes and the respiratory tract and a trigger of asthma attacks - nonetheless undesirable for that, of course.

There is no such thing as "a clean burn" where carbon fuels are concerned. Burning bio-diesel produces CO2, just as we produce CO2 when we "burn" the bio-oil direct. The proper way to compare fuels is to look at the complete life cycle of the fuel from production to use in vehicle. In the case of bio-diesel, CO2 is emitted in production and use, but the quantity produced in use is discounted against the quantity of CO2, absorbed by the parent plant (soya, sunflower, rapeseed etc.) in its life cycle. Overall, rapeseed bio-diesel emits half the net CO2 as mineral diesel.

As for emissions of the serious pollutants CO and NOx, rapeseed bio-diesel has slightly greater emissions than mineral diesel. But perhaps the most awkward fact is that current work on rapeseed diesel shows that it emits about twice the particulates, as does mineral diesel. It is not yet known if these particles are as dangerous as those from mineral diesel so far as their chemical composition is concerned. In this respect, the gas fuels Liquid Petroleum Gas (LPG) and Compressed Natural Gas (CNG) score well, as they produce practically no particulates.

The statements about consumption and adaptations are inaccurate. Consumption of rapeseed bio-diesel is slightly higher (about five per cent) than for conventional diesel. The fuel has also some corrosive action on rubber hoses but low-cost substitutes are available.

Nothing of the above is meant to suggest that the case for bio-diesel is a weak one. On the contrary, we think it is strong enough not to require overblown claims to aid its adoption as part of our drive to cut back on CO2 emissions; even if it can only be a small part if we tap just local sources of raw material. These were reckoned to provide around 1,000 tonnes of bio-diesel annually. In the year 2000, around 80,000 tonnes of diesel were used in the land transport sector.