Bristol has been named as the place where air pollution has increased the most since the first lockdown.
It follows a new report by the Centre for Cities which warns that toxic air is set to rise significantly as lockdown restrictions end.
Plymouth, Swindon and Exeter also appear in the top 10 worst affected by September coming third, sixth and ninth respectively.
The research body is now urging local authorities to take action to push levels back down to that seen prior to the pandemic.
Earlier in the year Bristol City Council announced it was looking to find an alternative to its current plans for a clean air zone.
The Centre for Cities says the use of private cars is the main cause of toxic air, with pollution increasing since May in line with initial restrictions easing. Meanwhile the centre says the use of public transport has remained low.
The research body is now calling for councils to:
Discourage car usage by introducing clean air zones that charge drivers
Encourage more public transport usage through improvements to bus, rail and tram systems
Improve cycling and walking infrastructure to encourage more active forms of travel
Centre for Cities’ chief executive Andrew Carter said: “City leaders can reduce threat of air pollution, but it will take political will.
"Discouraging car usage will be unpopular in the short-term but, if coupled with the necessary improvements to public transport, the long-term benefits to public health and the economy will be huge and our cities will become better places to live.
"Now is not the time for politicians to delay on this."
Bristol City Council has been approached for a comment.