Air quality has improved so much that environment chiefs will stop monitoring it in areas near the M1 and M25.

Maximum nitrogen dioxide (NO2) levels at six sites were below the legal limit in each year since 2018, according to Hertsmere Borough Council.

The gas, produced in vehicle engines, is linked with childhood asthma, diabetes, lung cancer, low birth weight and dementia.

Public Health England estimated six years ago that NO2 impacts would cost public healthcare systems £60.8million by 2025.

At a meeting on Wednesday, April 17, Hertsmere's cabinet member for environmental sustainability Councillor Paul Richards (LD, Bushey North) said: "This is a good news story."

He added: "During Covid, we all welcomed the chance as a silver lining of breathing a lot fresher air, in the absence of a lot of traffic.

"Since Covid restrictions have been lifted, we have found the improvements to the NO2 levels… have continued to be of a satisfactory level.

"We don't take air quality for granted here.

"Subject to further reports which will come to cabinet, we are looking at a borough-wide air quality strategy.

"We think this is important.

"The priorities have changed somewhat with the increasing move to electric vehicles.

"With the improvement to engine technology, there are aspects of air quality which have shifted slightly."

Cllr Richards said log burners and types of particulate matter from tyre wear remain air quality concerns.

Cllr Christian Gray (Lab, Potters Bar Furzefield), who is also a cabinet member, said: "It's a good news story that our air quality is much improved."

The cabinet agreed to retire six Air Quality Management Areas (AQMAs).

Hertsmere Borough Council has equipment in each area which measures levels of NO2.

The legal maximum is 40 micrograms of NO2 per cubic metre (µg/m3).

At 31-39 Blanche Lane in South Mimms, next to the M25 west of South Mimms Services, NO2 levels hit 39µg/m3 in 2019.

This fell to 30.3µg/m3 in 2023, a draft figure which could fall further after a bias adjustment process.

At Hartspring Lane, east of the M1 near Berrygrove, NO2 levels hit a 35.3µg/m3 maximum in 2019, before they fell to 33.2µg/m3 before the adjustment process in 2023.

West of M25 junction 24 at Potters Bar, Hertsmere Borough Council measured 32.8µg/m3 in 2018 and 26.8µg/m3 in 2023 – slightly up from 22µg/m3 in 2021, a year when Covid-19 restrictions were in place.

A monitoring point at the M25 and A1(M) junction for South Mimms Services recorded 32.5µg/m3 in 2018, rising slightly to 32.6µg/m3 in 2022 then falling to 32.1µg/m3 in 2023.