Five years on from its launch, the one-millionth car has been fitted with PSA Peugeot Citroen's patented diesel particulate filter (DPF), in a sign of the growing maturity of the emission control technology.

The technology got off to a steady start, with the 500,000th DPF being fitted in June 2003.

Since then, however, deployment of the technology has accelerated dramatically, and it is fitted on a wide range of Peugeot and Citroen models.

Peugeot's 206, 307, 307 and 607 models are all equipped with the filter, as are the Citroen C4, C5, C8 and Xsara Picasso.

Furthermore, PSA Peugeot Citroen has announced plans to expand the range of cars fitted with the filters even further in the coming months, with continuing improvements in the technology augmenting its efficiency and performance.

DPFs ensure that HDi engines equipped with the technology are among the world's cleanest combustion engines by dramatically curbing harmful greenhouse emissions.