In a study conducted for the Centre for Science and Environment, Swedish consultants Peter Ahlvik and Ake Brandberg at Ecotraffic have found that after taking into account all the toxic components in emissions the cancer potency level of diesel cars is double that of petrol cars in India. If only particulate emissions are compared from different car models then the cancerous effect of diesel particulate matter ( pm) from one new diesel car is equal to that of 24 new petrol cars and 81 compressed natural gas ( cng ) cars on roads.

The results of this study are further supported by evidence from another study conducted by the German Federal Environment Agency ( uba ). They have found diesel to be several dozen times more cancer-causing than petrol. Diesel particles alone constitute as much as 95 per cent of the cancer-causing potential of all diesel emissions, it reported. Differences in the cancer potency of vehicles can arise because of different fuel quality, engine technology and local temperatures.

Following the spate of epidemiological studies linking pm from diesel exhaust to increased lung cancer risk, the California Air Resources Board ( carb ) in 1998 labelled diesel particles as