The Centre for Science and Environment (CSE) analysed the emission data available on a sample of in-use vehicles tested by the Automotive Research Association of India (ARAI), Pune, before and after service. The analysis shows that about one-fifth of the four-wheelers (1986-1992 models) tested contribute 40 per cent of the carbon monoxide (CO), and two-fifth contribute nearly 70 per cent.

This means about 20 per cent of cars can bring down the carbon monoxide (CO) levels by 40 per cent. The next batch (another 20 per cent) would reduce emissions by 25 per cent. This analysis implies that about 40 per cent of vehicles contribute to nearly 70 per cent of the pollution load as opposed to the developed country scenario where 10 per cent of cars cause 60 per cent of the pollution. Also, instead of targeting all vehicles, it is important to target gross polluters but because of poor manufacturing, a lot more vehicles would have to be phased out in India for a desired impact on air quality.

Similar is the case with hydrocarbons (HC). About one-fifth of the 4-wheelers contribute over 40 per cent of the HC pollution load (see graph: Graphic details ).

Normally, it is found that vehicles tend to pollute more with age. But the CSE study found that emissions do not appear to be strongly related with age. A lot of the new vehicles are also quite polluting. The high emitters span across all model years, with relatively little contribution to pollution often from older vehicles. Vehicles tested by ARAI belonged to the model years of 1986, 1987, 1989, 1990, 1991 and 1992. Emission levels of all these models show that gross polluters occur in all age groups. In a few cases, 1991 models were found to be more polluting than 1986 models.

But the ARAI does not show this dimension in their study presumably because it would question the manufacturing capabilities of car companies. They only used their survey to conclude that I&M helps to bring down the overall pollution load.