Legal proceedings over air quality could herald more LEZs

The prospect of more and tighter low emission zones (LEZs) in British cities has been raised by the decision of the European Commission to launch legal proceedings against the UK for breaching air pollution limits.

Nitrogen dioxide (NO2) levels in conurbations including Greater London, Greater Manchester, the West Midlands, Merseyside and Glasgow are unacceptably high.

While London has an LEZ which focuses on medium and heavy-duty diesel-engined vehicles, the main emphasis so far within it has been on the reduction of particulate emissions: and engines which are very clean as far as particulate matter is concerned are often large producers of NO2.

The situation is further complicated because the Euro emissions standards do not measure NO2 as a discrete entity. They do measure NOx, which covers both NO2 and nitric oxide (NO) gases, and both gases are produced whenever combustion takes place in a nitrogen-rich atmosphere such as Earth’s.

They are also produced naturally, by lightning for example. Efficient and otherwise clean high-temperature combustion tends to produce more NOx gases than inefficient, low-temperature ‘dirty’ combustion; hence the use of exhaust gas recirculation to reduce combustion peak temperatures in modern diesel engines.

NO2 is said to cause lung inflammation and is of particular concern to patients suffering from asthma.

Several other EU member states, including France, Sweden, Denmark and Greece, also exceed the limits, but the UK is the first state to be prosecuted.

“Our priority is to protect public health and the environment,” European Commission spokesman Joe Hennon has told the BBC. “We think that’s what the people of the UK would want as well.”

Besides raising the prospect of more, and more stringent, LEZs in British cities, the prosecution may also encourage the authorities to curb the marketing and use of devices which bypass the SCR NOx-control systems on Euro 4, 5 and 6 trucks and buses.