Re: Ken Pumford's response ('Letters', #156) to my article ('Breathing is harmful to health', #155). Promoters of diesel have long argued that because diesel is more fuel efficient than petrol it produces less carbon dioxide and is therefore more climate friendly. This claim may not be true. A study by the Swedish Environmental Protection Agency says that although diesel cars use 20 to 25 percent less fuel than petrol, they emit 15 percent more carbon dioxide (CO2) per litre of fuel than petrol. As a result the overall effect of CO2 emission is negligible. In another study, Mark Z Jacobson from Stanford University has used computer simulations to prove that although diesel cars obtain better mileage and emit less CO2 than similar gasoline cars, they can emit 25 to 400 times more mass of particulate black carbon and associated organic matter ("soot") per km. The warming due to soot may more than offset the cooling due to reduced carbon dioxide emissions. It\'s not just global climate but also local pollution caused by diesel exhaust that is raising concerns, even in Europe. In the past few years in Paris, home of Peugeot, the world's leading manufacturer of diesel engines, levels of nitrogen oxides and ozone (which mainly result from diesel engines) have gone up to dangerous levels several times forcing authorities to send out pollution alerts and restrict vehicle movement. Similarly, according to a WHO report, 6 percent of all deaths in Austria, France and Switzerland are due to PM10 (again mainly caused by diesel engines).

Manufacturers in Europe may be developing "clean" diesel engines but it will be years before these technologies and the corresponding ultra-low sulphur fuel come to Nepal. We do not have to ban all diesel vehicles but at least admit that they are dirty and keep them at a safe distance from sensitive areas such as Kathmandu.

Bhusan Tuladhar,
Clean Energy Nepal