Portsmouth air pollution has risen slightly, but long-term levels continue falling

A “slight uptick” in Portsmouth’s air pollution has been recorded despite long-term improvements, with councillors told “we need to keep an eye on it”.

Portsmouth City Council’s cabinet member for climate change, councillor Kimberly Barrett, reviewed the annual air quality report for 2025.

Introducing the report, Richard Lee, the council’s assistant director of culture, leisure and regulatory services, confirmed the data, which covers the 2025 calendar year, had been validated by DEFRA.

While the vast majority of tests met national standards, he described 2025 as “less favourable” than 2023 due to increases in nitrogen dioxide and particulate matter pollution.

Nitrogen dioxide (NO2) is a harmful gas mainly produced by vehicle exhausts, which can irritate airways and worsen respiratory conditions.

Particulate matter (PM) consists of tiny airborne particles from sources including traffic, industry and wood burning. These can penetrate the lungs and, in some cases, enter the bloodstream.

Of 228 diffusion tubes across the city, only one exceeded NO2 standards, at Alfred Road in the city centre. Despite this, the location does not allow for “long term exposure” to residents.

Some 176 diffusion tubes, representing 77 per cent of testing sites, recorded increases in NO2 levels between 2024 and 2025. However, over a five-year period, 225 tubes showed a downward trend.

Of the six higher-tech continuous monitoring stations across the city, all of which complied with national standards, four recorded slight increases in NO2 levels.

There were also increases in particulate matter, although all measurements remained within national standards.

The largest increases were in particles smaller than 10 micrometres (PM10) at London Road and Alfred Road.

Levels of the smaller particulate matter (PM2.5) in London Road were “close to” breaching the national standard.

Mr Lee said there were no proposals to remove the city’s air quality management areas (AQMAs), due to the “slight uptick” in pollution.

AQMAs had partly led to the introduction of the Clean Air Zone in the south-west of the city in 2021, which charges non-compliant vehicles when driving through it.

However, he added: “I do think there will come a time when we’ll talk about revoking them”.

Regarding the increase in pollution, Mr Lee said he could not say “why it occurred” but highlighted that there is rarely a “nice linear line in terms of improvement” in national air quality data.

“We need to keep an eye on it – we need to understand if 2025 was an unusual year or if it’s part of the seasonal variation in terms of improvement.”

Cllr Kimberley Barrett thanked Mr Lee for his work, which took six months of preparation before being submitted to the Government for validation.

“The long term trend is good even with that small uptick – people will ask questions as to why this has happened and colleagues across the council will be having a look”.

More information you can read the report here.