From correspondents in Delhi, India, 11:32 PM IST

Of all the interventions made to clean Delhi's air, conversion of diesel buses to compressed natural gas has been the most important, a new study by a Washington based organisation revealed Thursday.

The Resources for the Future (RFF), a non-profit research organisation, in its study has assessed the impact of various pollution control measures on air quality trends in Delhi over a 15-year period (1990-2005) and found that CNG programme has made the most significant impact.

'Delhi's CNG programme has made a huge difference to air quality, but these gains will be lost if the kilometres travelled by all vehicles continue to grow,' said Urvashi Narain, a fellow at RFF and one of the study's co-authors while releasing the results in the capital.

Conversion of buses to CNG is important because buses travel more kilometres in the city and contribute more to the pollution load, the study says.

It says that CNG buses have helped reduce respiratory suspended particulate matter (RSPM), carbon monoxide (CO) and sulphur dioxide (SO2). Also, it has not contributed to an increase in nitrogen dioxide (NO2).

Of the other interventions, the reduction of sulphur in diesel and petrol has also had a significant impact.

The study advises other Asian cities to consider the gains that can be made by switching fuels - moving from diesel or petrol to CNG - as this single intervention can have significant impact.

Underlining the stricter emission standards for diesel cars, the study says that rise in the number of diesel-operated cars, leads to increase in NO2.

(Staff Writer, © IANS)