Pollution from many popular diesel cars is much worse when it is colder than 18 degrees Celsius, according to new research reported by the BBC, raising the possibility that many makes of cars could be circumventing European rules on emissions.
Emissions Analytics, an emissions testing company, told the U.K. broadcaster that it had tested 213 models across 31 manufacturers and had found a "significant rise in poisonous gas emissions from a wide range of car models as the temperature drops," the BBC said in its report published on Tuesday.
The problem was apparently worst among the "Euro 5" category of cars pertaining to light passenger and commercial petrol and diesel vehicles.
European standards have laid down rules on the construction of motor vehicles relating to the emission of atmospheric pollutants (both particulates and nitrogen oxides which could pose the most risk to health) from vehicles.
The EU has sought to reduce emissions and improve air quality, particularly as sales of diesel vehicles have increased. However, manufacturers are allowed to cut back on pollution controls as long as it is to protect the engine, the BBC noted, and have potentially taken advantage of such allowances to get around emissions.
"The finding means that millions of vehicles could be driving around much of the time with their pollution controls partly turned off," the BBC said. "But it seems many cars are deliberately designed that way and it is all perfectly legal," the BBC added.