Pollutionwatch: exhaust emissions double below 20C – by design

Twenty-five years ago, starting a car in winter required careful balancing of choke and accelerator and sometimes sprays of WD40 or a bump start. Now, modern vehicles simply work in the cold. However, a European parliament inquiry following the Volkswagen scandal found that the nitrogen oxides abatement systems on many diesel cars shut down below the official test temperature of 20C. Manufacturers say that this prevents engine damage and is therefore legal. Real-world driving measurements on 9,000 cars in Gothenburg, Sweden, have shown this shutdown in action. Average emissions at 10C were almost twice those at 25C.

Some cars have exhaust controls that operate effectively in the cold so the problem is not a technological limitation but a design choice. If cars can be built to start on a damp, cold January morning then why are their exhaust controls not designed to work in winter conditions? The effectiveness of exhaust controls has also been called into question by recent Department for Transport inspections that found 8% of lorries had cheat devices fitted; 20% for those registered in Northern Ireland, but less than 5% for non-UK lorries.