Urban cycle tests carried out on petrol and diesel-powered cars of comparable power ratings by a European environment and energy research programme have produced the surprising result that the petrol vehicle was the most heavily polluting.

The 1.6l petrol car produced twice the volume of ozone emissions of the 1.9l diesel, both being equipped with catalytic conversion devices, on a rolling road programme simulating urban driving conditions. Tests were carried out at different effective speeds. In stop-start conditions, the diesel's pollutant emissions ranged between 0-5% while those of the petrol car ranged from 10-15%.

On the other hand, the diesel car in the test was let down by its particulate emissions, notwithstanding the fitment of the PSA Peugeot Citroen filter, which traps 90% of particulate emissions. Such filters are likely to become the norm on new diesel cars from next year, when Euro 4 emissions limits halve the current permitted emissions of particulates. (Source: CCFA, the French vehicle manufacturers' association)