The Environment Agency has confirmed that it has identified the source of a 'mystery' smell that has been lingering over Darlington and parts of County Durham. 

A sulphur 'gas-like' smell has been frustrating locals from North Darlington up to Newton Aycliffe since September time.

Some residents have been baffled about what the cause of the smell was - which some described as "horrendous" and "off-putting". 

One Darlington mum, who wished to remain anonymous, said she first became aware of the smell on December 4 outside her home in the town.

The Northern Echo: Aycliffe town centreAycliffe town centre (Image: NORTHERN ECHO)

She said: "I first smelt it outside my home but later everything clicked and I realised that I had smelt it before when I had been travelling up and down the A1. 

"I had been saying to my husband that it was going around Darlington in certain areas but it's been three weeks that I've smelt it now.

"But, when we were over in Aycliffe for an event about a week later, I got another whiff of it. It got stronger and stronger as we got nearer to the A1."

The Northern Echo: A woman with her fingers covering her noseA woman with her fingers covering her nose (Image: PA MEDIA)

Asked to describe the smell, she said it's like a "metallic sulphur" scent.

She added: "When it hit me, it made me feel a little bit sick, and I've not wanted to leave the house because of it.

"We should be breathing in clean air - not that. Is this harmful? Is there anything in this that could harm us and my children?"

The Northern Echo: Darlington town centreDarlington town centre (Image: NORTHERN ECHO)

Meanwhile, other people on social media have become "sick" of the smell - which they have smelt on the A1(M) whilst travelling between Darlington and Aycliffe. 

Despite the concerns of residents, both on social media and in person, the Environment Agency has now pinpointed the source of the whiff. 

The Northern Echo: A landfill siteA landfill site (Image: PA MEDIA)

Confirming the location of the smell, officers from the Agency have narrowed it down to the Aycliffe Quarry Landfill site and have committed to working with the business on reducing the smell that emanates from it.

An Environment Agency spokesperson said: “Together with our partners at Durham County Council and Darlington Borough Council, we’ve been investigating odour issues in Newton Aycliffe and Darlington since September and our enquiries have found the odours are coming from the Aycliffe Quarry Landfill site.

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"The operator does have a landfill gas extraction system and we have instructed them to make improvements to this system.

“They have provided us with a programme of work which started in early November and includes installing additional gas extraction wells and capping work to seal in the waste.

"We understand these odours are not pleasant for the community and we are monitoring the progress and effectiveness of this work. We expect that as it progresses the frequency and intensity of the odour will diminish.”