Air pollution rises inside city's clean air zone

An increase in air pollution inside a clean air zone (CAZ) is down to the impact of weather, a local council has said.

New data has revealed that nitrogen dioxide levels rose on average by 2.4% inside Bristol's CAZ in 2025 compared to the previous year.

Bristol City Council said the recent increase was down to weather factors, which was mirrored in other parts of the country.

Pollution levels have still fallen by 16% since charges on non-compliant vehicles were introduced in 2022, which the local authority said was "the most important measure of progress".

The council said that wind and rain can help clear pollution, but calm, still weather can trap nitrogen dioxide close to the ground, contributing to a perceived increase.

Enda Hayes, professor of air quality and carbon management at the University of the West of England (UWE), said one year of data should be interpreted "cautiously".

"Low wind speeds, stable atmospheric conditions, and less dispersion can increase NO2 concentrations even when emissions remain unchanged or continue to fall," he said.

"It would be difficult to interpret such a modest change as evidence of a reversal in the longer-term trend, particularly when concentrations remain substantially below pre-CAZ levels."

Bristol's CAZ has to remain in place until all the monitoring sites fall between the nitrogen dioxide legal limit of 40μg/m3.

The council said all of the nine sites still above this level were in a small area of the city centre.

The number of compliant journeys through the CAZ also rose from 89% in 2024 to 93% in 2025.

Councillor Abi Finch, chair of the Environment and Sustainability Committee, said the increase was "minimal" and "does not diminish the overall reduction in air pollution we have seen since 2022".

"Better air quality benefits everyone, but particularly children, older people, pregnant women, people with existing health conditions and more disadvantaged communities," she said.

"While I understand there will be some frustration with the increase between 2024 and 2025, the detrimental impacts of nitrogen dioxide are why we must continue to keep pushing to make progress and not be disheartened by the slight increase in air pollution from 2024 to 2025.

"We will continue monitoring pollution hotspots, supporting sustainable travel and I encourage any residents or businesses who are driving non-compliant vehicles to please apply for our financial assistance scheme."

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