Hot air in diesel's eco-hype

The transformation of diesel’s reputation—from a sooty stain on the environment to the saviour of the planet—has taken place remarkably fast. This 180-degree turnabout became complete last month when BMW distributed half-a-million copies of a four-page, glossy brochure in the Sunday Times touting its new diesel X5 SUV as a solution to the greenhouse-gas effect.

Along with a photograph of a snow-capped mountain, BMW’s marketers wrote: “With xDrive you’ll get to see it. And with Ultra Low Sulphur Diesel the next generation gets to see it too.”

The new diesel eco-hype is everywhere. Advertisements for Engen’s Dynamic Diesel feature an image of flowers blooming out of a fuel-pump nozzle. The website for Volkswagen South Africa claims that with its “environmentally friendly” diesel engines “you can drive with a cleaner conscience, not just a cleaner engine”.

But the dirty reality is that South African diesel fuel and diesel vehicles do not live up to this squeaky-clean image. Compared with petrol cars, oil-burners emit far more smog-forming nitrogen oxides and carcinogenic particulates.

Their advantage in greenhouse-gas emissions is also consistently overestimated. In fact, under some circumstances peculiar to South Africa, a diesel car may actually send more greenhouse gases skyward than a comparable petrol car. According to Don Anair, an American diesel-emissions specialist with the influential Union of Concerned Scientists, “the cleanest diesel vehicles are still not as clean as the cleanest gasoline vehicles”.

Sulphur levels

South African diesel fuel is less dirty than it was before 2006, when legal sulphur levels dropped from 3 000 parts per million (ppm) to 500ppm. But those current sulphur levels are still 10 times higher than would be allowed in most European or Australian diesel and 33 times higher than in the 15ppm sulphur diesel sold in the United States.

In South Africa, ultra-low-sulphur diesel with 50ppm of sulphur is becoming available at some Sasol, Shell, Total and BP filling stations, though not yet from Engen’s flowering pump nozzles. This cleaner, more expensive diesel makes up only 3% of diesel sales, despite the recommendation from manufacturers that owners of their newest diesel models fill up with the pricier diesel. In fact, the most sophisticated diesels on the market, such as Honda’s CR-V and BMW’s X5sd, can only use ultra-low-sulphur diesel.

Fuel retailers have muddled consumers by failing to distinguish between the two diesels as they promote their brands. Total South Africa, for example, calls both types of diesel “Ecodiesel”, adding the word “Premium” to the 50ppm variety. Last month, the National Association of Automobile Manufacturers of South Africa issued a “diesel fuel quality advisory” complaining that fuel retailers fail consistently to make it clear at the pump which fuels have 500ppm or 50ppm of sulphur.

“Meanwhile, we are being bombarded by advertising claims about ‘our clean diesel’,” says Stuart Rayner, chairperson of the association’s fuel and emissions committee. “If you were to believe the advertising,” he adds, a consumer would think that all diesel is now clean.

Diesel cars are also falling short of their green hype. Volkswagen’s website fails to mention that its “environmentally friendly” diesel vehicles had to be removed from the American market this year because they could not live up to increasingly stringent US emissions standards. European regulations have always favoured diesel engines by allowing them higher levels of particulates and nitrogen-oxide emissions than expected from petrol vehicles.

Washington is levelling the playing field, holding diesel vehicles to the same emissions rules. As a result, Volkswagen, the leader in US diesel passenger-car sales, had to withhold its diesel vehicles while it sorts out the technology required to meet the standards. Other manufacturers, from BMW to Volvo, have delayed introducing diesel cars into the US market for the same reason.


South Africa is following Europe’s regulatory lead, though at a laggard’s pace. Starting in January of next year, all new vehicles will have to meet emissions standards known as “Euro 2”. These diesel-biased regulations were implemented in Europe 12 years ago. The Europeans have since move on past Euro 3 to Euro 4. Under those current European Union regulations, vehicles must emit no more than one-quarter of the particulates allowed under the new South African limits.

Particulates, sometimes called soot, are the most visible of pollutants. Every winter, Dr Ivan Toms, executive director of health for the City of Cape Town, sees them writ large. “If you come over Wynberg Hill, you get a nice view over the city, but you look down and see this horrible brown layer of polluted air trapped under a layer of warmer air,” he notes. “It looks terrible.”

Diesel emissions account for 42% of the Mother City’s infamous brown haze, more than any other source measured by the University of Cape Town’s landmark Brown Haze I study. (Near Khayelitsha informal settlement, however, smoke from wood fires plays a larger role.)

Eugene Cairncross, an air-pollution specialist at Cape Peninsula University of Technology, says that dropping diesel sulphur levels to 500ppm did not go far enough to address the problem. “Although it has dropped emissions a bit,” says the chemical-engineering professor, “the problem hasn’t gone away.” Only with expensive particulate filters and ultra-low-sulphur diesel can the fuel’s contribution to particulate pollution be conquered.

Particulates do more than spoil the view. A report in the August issue of the South African Medical Journal estimates that particulates in outdoor air pollution lead to 4 637 premature deaths in South Africa each year, largely from cancer, strokes and heart attacks. The study calculates that particulate matter in major South African cities is on average more than three times higher than safe levels.

As diesel sulphur levels have fallen and engine technology has improved, sooty exhausts have become a rarer sight behind passenger cars. But Cairncross says that does not mean that South Africans can breathe easy. “The fact that in some cases you can’t see it doesn’t mean that it’s not coming out,” he says.

In fact, less visible particles below 2,5 microns in diameter are the most dangerous. “At one micron, they are not visible at all, but they can penetrate deep into your lungs and cross into the bloodstream,” adds Cairncross, a co-author of the South African Medical Journal study. Smaller particulates also disperse farther in the air, affecting people living well away from highway congestion and industry.

Reducing emissions

These problems are all local, however, and some would argue that the far-reaching impact of global warming means that some diesel pollution must be tolerated. But diesel’s potential for reducing greenhouse-gas emissions is regularly overstated. BMW’s X5 brochure, for example, notes that its diesel model uses “up to a quarter less fuel than its competitors”, including the equivalent petrol X5. It adds that this “of course, means a reduction in the greenhouse gases responsible for global warming”.

One little-known reason for diesel’s superior efficiency, however, is that the fuel is denser than petrol, with more carbon. As a result, litre for litre it gives off more Earth-warming carbon dioxide when burned. So in measuring the grams of carbon dioxide per kilometre, Britain’s Vehicle Certification Agency finds that the X5 3.0sd diesel is only 11% better for the atmosphere than the petrol version, despite having 25% better fuel economy. Fuel consumption “is only really useful in terms of amount of money you’re going to spend on fuel”, notes Frank Schwegler, president of South Africa’s National Association for Clean Air, “but greenhouse-gas emissions is quite a big factor to consider.”

For now, finding a car’s carbon-dioxide emissions per kilometre at a dealership requires scrutinising the fine print of a technical specifications sheet, if the figure is there at all. Starting in mid-2008, however, all new cars in South Africa will have to display this number—as well as litres per 100km—based on standardised measurements that can be compared between brands.

In the meantime, the Union of Concerned Scientists suggests that car shoppers should adjust a diesel car’s litres-per-100-km figure upward by 18%. Comparing the resulting figure with the fuel economy of a petrol vehicle puts the two on an equal footing as far as greenhouse-gas emissions are concerned.

Even after those adjustments, diesel engines remain somewhat more efficient than their petrol counterparts. And with cleaner Euro 3- and Euro 4-compliant vehicles arriving now in showrooms, some environmentally conscious consumers may decide to tolerate diesel’s local pollution—or the high cost of effective emission controls—in exchange for the lower greenhouse-gas emissions. As if that decision was not complicated enough, a more vexing quandary faces diesel buyers at the filling station.

Since Sasol’s coal-to-liquids plant in Secunda is the largest source of ultra-low-sulphur diesel in South Africa, opting for 50ppm sulphur diesel over ordinary 500ppm actually quadruples the chances that the fuel in the pump is coal-based.

Sasol’s Fischer Tropsch coal-to-liquids process is an incredibly dirty way to make an incredibly clean fuel. Every drop of diesel that the company makes from coal is so low in sulphur—approximately 10 ppm—that it could be sold in virtually any country in the world.

But the Secunda facility emits about 60-million tonnes of carbon dioxide into the atmosphere each year. That’s barely less than the greenhouse-gas emissions for all of Israel and its seven million people. In making a litre of coal-to-liquids diesel or petrol, Sasol sends well more than 3kg of greenhouse gases into the atmosphere, far more than a car will emit while driving on that litre.

Sasol already supplies half of all the ultra-low-sulphur diesel sold in South Africa, and it is the best situated to increase supply as demand rises. Bizarrely, Sasol has to sell most of its clean diesel as regular 500ppm sulphur diesel for a lower price; demand for 50ppm is not yet high enough. As sales of “green” diesel cars grow, Sasol can sell that same fuel for more money as ultra-low-sulphur to take a dominant market share in the 50ppm segment.

It will be a sad irony when most of the millions of tonnes of greenhouse gases spewed by Sasol to make diesel is paid for by the drivers who bought the most “environmentally friendly” cars.

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