Fewer of the most polluting vehicles were recorded in Sheffield’s Clean Air Zone over the past year, but faulty technology in diesel buses has failed to meet emissions standards.

The first Sheffield City Council report showed between November 2022 and October 2023 the number of the most heavily polluting HGVs, buses and taxis fell by two-thirds both within the CAZ and across the city as a whole.

But catalytic reduction technology retrofitted in the city’s buses is failing to perform at the desired standard for reducing emissions. 

In a statement to Parliament on Tuesday, Paul Blomfield, Labour MP for Sheffield Central, said: “The main problem with the retrofit devices running in urban areas is that they do not reach the required temperatures to treat emissions as a result of the regular stop-start conditions. 

“That happens significantly when buses run downhill, and anybody who knows Sheffield knows that there are a lot of hills to run down.”

Altogether 75% of the city’s 400 buses have been retrofitted with the technology, but still do not comply with the desired Euro 6 standard. 

The remaining 25% have had no technology installed and so still release the same levels of harmful emissions. 

Mr Blomfield is now imploring the government to fund the roll-out of hydrogen and electric buses in Sheffield. 

The CAZ was introduced in February to tackle Sheffield’s dangerously high levels of nitrogen dioxide, which contribute up to 500 deaths per year according to a 2010 NHS report. 

Despite failures with the buses, the data shows Private Hire Vehicles are now 96% compliant compared to 77% before the CAZ was launched and LGVs are now 84% compliant up from 59%.

Cllr Ben Miskell, Chair of the Transport, Regeneration and Climate Committee, said: “Hundreds of people in Sheffield die prematurely each year due to air pollution, cleaning up the quality of the air we breathe around Sheffield is rightly one of our top priorities and this data shows that motorists are helping by moving to cleaner vehicles in response to the Clean Air Zone.”

The CAZ currently fines highly-polluting lorries, vans, buses and taxis that drive within the boundary of the ring road, with charges ranging from £10 per day to £50 per day depending on the vehicle.

The scheme does not apply to private cars and motorbikes.

In November, the council announced the CAZ had currently raised over £3m in charges and fines for late payments.

However, this still falls short of its £4.25m implementation cost.