A street in Glasgow, known to be a pollution hot-spot, has seen Britain's biggest improvement in air quality since the coronavirus lockdown.
Nitrogen dioxide levels in Hope Street have fallen from 56.6 micrograms per cubic metre to 18.7.
Researchers studied readings from 32 sites in Scotland, Wales and England and compared them with "business as usual" figures.
Hope Street has consistently been one of the most polluted roads in Scotland.
The study was carried out by environmental consultancy Ricardo.
The air quality monitor is in a "street canyon" where it is surrounded by tall buildings with little wind to disperse pollution from the cars, buses and lorries which pass through.
But since lockdown restrictions were enforced, traffic there and across the UK has plummeted.
David Carslaw, technical director at Ricardo, said: "When we tend to think of air pollution we tend to think of things like low emissions zones and clean air zones where we generally try and change the vehicle technology.
"The Covid impact has very much been about reducing vehicle activity and that's a very different way of achieving the same sort of air quality benefits."
Not every site in Britain has been examined but the data does include those which are normally the most polluted.
Nicholson Street in Edinburgh has seen the second largest reduction followed by St Aldate's in Oxford, Marylebone Road in London and Hafod-yr-ynys in South Wales.
Dr Richard Dixon, from Friends of the Earth Scotland, said: "We need to see concerted action from councils and the Scottish government if we want these reductions in dangerous air pollution continued in a way that is fair to people and sustainable in the longer term."
Councillor Anna Richardson, Glasgow city convener for sustainability and carbon reduction, said: "The link between vehicle traffic and pollution is well understood and there has been an obvious reduction in vehicles moving around the city during lockdown.
"Making sure the gain in air quality made in recent months is not lost is part of the considerable challenge the council faces as we emerge from the covid-19 crisis."