Tiny particles emitted by petrol cars can cause health problems, and particle numbers (PN) have been regulated since a new standard, the Euro 5, became law in September 2009.

Testing was always done in a laboratory, which poorly represents how people drive in the real world.

After agreeing on a real driving emissions (RDE) test for nitrogen oxides, another type of pollutant, the European legislators are preparing to incorporate PN values in the new on-road test procedure.

However, a political controversy has emerged in Brussels after the European Commission proposed to let carmakers pass the test if the PN value was a factor 1.5 - in other words 150 percent - of the limit value.

This leniency is called the conformity factor.

On Tuesday (25 October), seven members of the European Parliament sent a protest letter to the legislative working group responsible for the details of the new test.

The letter, seen by this website, was signed by four centre-left MEPs, one Green MEP, and two Liberal MEPs.

"The commission’s proposed conformity factor of 1.5 is unnecessarily high,” they wrote.

But attendees of a real driving emissions conference held in Berlin on Tuesday and Wednesday, said the opposite.

They said the extra 50 percent leniency is necessary because the testing equipment is far from perfect.

This equipment, mounted on a car which is then taken on the road, is called Portable emissions measurement system (Pems).

Joachim Demuynck, scientific officer at the Association for Emissions Control by Catalyst referred to recent research by the European Commission's in-house science body, the Joint Research Centre (JRC).

“They have done tests with Pems equipment and compared it with the current lab equipment, and they observed this 50 percent deviation,” said Demuynck, whose association also tests with Pems equipment. He added their group also found similar results.

Even lab testing is difficult

Piotr Bielaczyc is head of the engine research department at Bosmal Automotive Research and Development Institute in Poland.

“Particulate number measurement is the most difficult. Not only on the road, also in the laboratory,” he said.

“There are two main equipment suppliers,” noted Bielaczyc.

“Even when we compare particulate matter equipment from these both companies on laboratory conditions we have different results: 10, 15 percent. In my opinion this uncertainty is still too high.”

One of the difficulties with measuring particles is that they are very, very small. In the real world, many more factors can influence the measurement than in a controlled laboratory.

50 percent margin 'not final'

European Commission spokeswoman Lucia Caudet sent EUobserver a written statement, defending the EU executive's proposal, which will need member states' consent.

“The 50 percent margin mirrors the uncertainty of the best equipment currently available in the market,” said Caudet.

“It is important to understand that the logic is that RDE testing is still subject to technical margins of uncertainty. As the technology improves, we will be able to reduce the 50 percent margin further.”

She noted that the commission proposed to include a review clause, so the 50 percent “cannot be considered as final”.

Several engineering expert at the Berlin conference noted that carmakers will make sure their cars stay within the limit, because their measurement equipment also has a possible error margin.

After the backlash created by the emissions fraud by Volkswagen Group, no one wants to take that risk any more.

The MEPs behind the protest letter are unconvinced, however.

They say that verification of particle emissions should be done “in a robust manner that promotes state-of-the-art technology”.

They note that gasoline particulate filters, which carmakers can add to their petrol cars, have “proven to be effective in removing almost all particle pollution, meaning the discussion surrounding conformity factors for particulate numbers is redundant”.

European Parliament excluded

Seb Dance, a Labour MEP from the UK, said the margin of error was “actually 30 percent”.

The legislation under preparation cannot be changed by MEPs. They only will be able to veto it.

However, they partly have themselves to thank for it.

In 2007, when the latest car emissions legislation was adopted, it included the option for the EU commission to create bills on real driving emissions without the input of the parliament.

This process is called comitology, and MEP Dance noted that “whilst there is an important role for delegating implementing powers to the commission, I do have serious concerns about the way some of these decisions are taken”.

He added that “substantial elements of existing legislation [are amended] through the backdoor in technical committees with essentially no oversight from the European Parliament of the discussions taking place”.

Part of the left-leaning MEPs' grudge may be explained by a previous experience with conformity factors.

A year ago, member states agreed to a temporary conformity factor of 2.1 for nitrogen oxides emissions. Those close to the negotiations agreed that this was a political compromise, rather than a scientific necessity.