Thanks for the very illuminating article ('Breathing is harmful to health, #155) about air pollution in Kathmandu Valley. Thanks also for creating a weekly space in your paper monitoring PM10 levels. As Mr Tuladhar's article so elegantly brings to the fore, the pollution alarm bells in the valley are deafening. Air pollution is a deadly problem in Kathmandu, and we are, in a typically Nepali fashion, waiting for disaster to strike to collectively say "Ke Garne". Actually it has already struck those who are suffering from exacerbations of chronic lung disease and are languishing in hospital beds as the article points out. We should be working together to save our ecology, our health, and our chronic lung patients from this dangerous vehicle exhaust, especially diesel. As Mr Tuladhar suggests people who drive heavy diesel- powered SUVs need to seriously consider switching to non-diesel. In addition, the government must urgently act to reduce pollution levels in our magnificent city.

Buddha Basnyat, MD
Kathmandu

. I would like to correct some of the information presented by Bhusan Tuladhar regarding diesel engines in his otherwise excellent article on particulate air pollution in Kathmandu. 'Environmentalists all over the world are now campaigning to ditch diesel' certainly isn't the situation in Europe, the home of the most sophisticated diesel engine technology in the world. Almost all European governments subsidise diesel vehicles via lower sales taxes on diesel vs petrol, and in the UK, where prices for the two fuels are the same, diesel demand is rapidly increasing due to a new tax that favors engines that deliver lower C02 emissions, i.e. diesels. Increasing diesel engine use in Euorpe is seen as a key strategy in achieving the CO2 emission reduction required by the Kyoto protocol on global warming. Fuel efficient diesel engines are installed in roughly 40 percent of all new cars sold in Europe and are expected to exceed 50 percent of sales by 2005. European diesels meet the stringent Euro III emission standards, and will soon be meeting the even tougher Euro IV and Euro V standards.

The common rail fuel injection systems, catalytic converters, and exhaust particulate filters required to meet the regulatory standards require diesel fuel with very low levels of sulphur, and herein lies the problem with use of modern diesels in Nepal. Even in some advanced countries outside of Europe, such as the US and Canada, sulphur levels in diesel fuel are 20 times higher than the 15 parts per million (ppm) maximum that European emissions control systems can tolerate.

Presumably sulphur levels in the diesel fuel available in Kathmandu are higher still. Until sulphur levels drop to the 15ppm range, no emission control system on a diesel would function for long in Kathmandu.

However, before dismissing diesels in Nepal, their benefits (even without a modern emissions control system) must also be considered. The primary benefit is increased fuel economy, typically 30 to 40 percent in real world conditions, which is accompanied by a corresponding reduction in CO2 emissions. It would be unfair and unwise to penalise all of Nepal by depriving the country of the savings that diesel engines offer just because of the special circumstances in Kathmandu that concentrate particulate emissions. Perhaps banning diesels from Kathmandu only is part of the answer to Kathmandu's particulate problem; however, a ban on diesels shouldn't be extended to the whole country.

Ken Pumford
Ford Motor Company
V Diesel Engineering
Dunton, UK