The move by the environmentalists is a step forward for the Nepali government's plans to lower the levels of air pollution in Kathmandu. The government has decided to ban polluting vehicles from Kathmandu by mid-July 2000. Nearly 70,000 vehicles, including two-wheelers, ply on the streets of this bowl-shaped valley. The threshold for emission has been set at three per cent carbon monoxide for petrol-driven vehicles and 65 Hetridge Smoke Unit (HSU) for diesel vehicles.

The programme to completely phase out polluting vehicles from the city's Ring Road area, the 27.3 km road that circles the core of Kathmandu, has been initiated to control the deteriorating air quality.

The government has planned to extend such emission-free zones by announcing new thoroughfares -- starting from mid-February next year -- which will come underrestricted zones. Currently there are a total of nine restricted areas in the capital city that bar vehicles which have failed emission tests.

Experts say if properly implemented, the programme would go a long way in improving the quality of air in the capital. Air pollution level at the moment is many times above the danger mark stipulated by the World Health Organisation (WHO). Vehicular emissions contribute a major chunk of the total suspended particulate matter (TSP) concentration in Kathmandu air.

Explorer Nepal, a non-governmental organisation, has asked city residents not to use an Indian-made heavy smoke belching three-wheeler. Results of emission tests show that most of these vehicles exceed the limits.

These diesel operated, 12-seater vehicles have been found to be Kathmandu's biggest pollutants. Most of them have more than 100 HSU emission, test results show. More than 3,000 of these vehicles ply throughout the city and, because of their cheap service, are popular among the common people.Not all agree with the blacklisting of such tempos. ``The phase-out programme will not be successful if the government does not come up with alternatives to these tempos,'' says Surendra Devkota, a member of the Environment Protection Council. ``The government should think about alternatives to tempos which, despite being major pollutants, have greatly been contributing to the easy mobility of thousands of commuters,'' he added.

Many four-wheel-drives, luxury cars and station wagons also considerably contribute to air pollution, experts say. ``At least 25 per cent of the luxury cars and jeeps fail emission tests,'' says an official at the Emission Test Unit of Valley Police.

Dust particles too contribute to the deteriorating air quality. A study being carried out by the Nepal Environment and Scientific Society (NESS), a non-governmental research organisation, has revealed that dust contributes almost 40 per cent to air pollution here. ``Two months of our study has shown that dust is a major cause of airpollution, second only to vehicular emission,'' says Toran Sharma of NESS.