SCOTLAND’S towns and cities have seen a “stark decrease” in toxic traffic fumes since the coronavirus lockdown came into force. 

Busy roads in places such as Glasgow, Greenock and Fort William have all seen nitrogen dioxide levels more than halved.

It comes amid calls for radical rethink of public transport and car use after the restrictions are lifted. 

Plans to introduce low-emission zones (LEZs) in four of Scotland’s cities have been put on hold because of the outbreak.

The new data was published by Edinburgh University’s Professor Paul Palmer and Dr Douglas Finch in a blog post for the Scottish Parliament Information Centre.

They said: “This period of enforced traffic reduction has given us an opportunity to see what our cities would be like with reduced emissions. How air quality changes over Scotland and the rest of the world as the lockdown continues will be extremely interesting and no doubt the subject of many research projects.”

Combustion engines emit nitrogen dioxide (NO2), volatile organic compounds (VOCs) and particulate matter (PM) among other pollutants.

All of these are known to have adverse effect on the respiratory system, including reduced immunity to lung infections, which the academics said “is particularly relevant to the Covid-19 virus”.

To track changes, they used air pollution measurements from the Department for Environment, Food and Rural Affairs’ Automatic Urban and Rural Network (AURN). 

They said there are 19 sites operating in Scotland, scattered among urban and rural locations. 

The academics said: “If we look at a typical week of nitrogen dioxide concentrations in Glasgow, we can see the lockdown has led to a stark decrease in emissions. 

“During a normal, pre-lockdown week, variations in nitrogen dioxide concentrations reflect traffic patterns, with a daily cycle peaking at morning rush hour and a smaller peak for the evening rush hour. 

“There are lower concentrations at the weekend due to less traffic on the roads. 

“During the lockdown, there is still a morning rush hour but nitrogen dioxide levels are substantially lower for every day of the week, lower than values we normally expect on a Sunday.”

They said a similar pattern could be seen across cities in Scotland, as well as the rest of the UK. 

However, analysis of other pollutants paints a more complicated picture. 

The level of PM2.5 (particulate matter smaller than 2.5 microns), for example, has not shown “a clear directional change” – and even increased early in the lockdown.

The academics said: “One potential explanation for this is the influence wind has on particulate matter. A new weather system arrived over the UK at the same time as the lockdown came into force and caused a change in wind direction over much of the country. 

“This meant air was being brought from the east (from continental Europe) that may have been more polluted than air blown in from the west.”

They said another explanation could be “an increase in barbecues and garden bonfires occurring due to the warmer weather and people staying at home”, although this is difficult to confirm.

The experts said the analysis showed “traffic is not the only consideration when cleaning up our air”. 

They added: “Variations in PM2.5 concentrations have highlighted that changes in local emissions do not exclusively control local pollution levels.  

“As emissions from newer vehicle fleets get progressively cleaner we will likely need to shift our focus on to other pollutants. For instance particulate matter smaller than one millionth of a metre that can penetrate further into the human body.

“By adopting cleaner travel options, such as more electrically powered transport and more cycling and walking infrastructure, then we would see lower levels of nitrogen dioxide.”

LEZs were due to have been brought in later this year in Edinburgh, Aberdeen and Dundee, while the first scheme in Glasgow was expected to be fully implemented, but Transport Secretary Michael Matheson has now said this is “no longer practicable”.

He stressed the Scottish Government is fully committed to tackling the problem of air pollution, but he confirmed the implementation of LEZs has been paused.

It followed a decision by members of the Low Emission Zone Leadership Group, which includes Mr Matheson and Environment Secretary Roseanna Cunningham, as well as representatives of the four councils involved, Public Health Scotland and environmental watchdogs at the Scottish Environment Protection Agency.

Ministers hope delaying the implementation of LEZs will give those involved the chance to consider what transport systems could look like after Covid-19.

Mr Matheson said: “The Scottish Government is fully committed to tackling air pollution in the quickest time possible.”

But he added the “unprecedented impact of the Covid-19 outbreak has resulted in necessary changes to priorities across government and across our local authority partners”.

The Transport Secretary continued: “Similar to other initiatives across public sector, we have come to the view that introducing low-emission zones across our four biggest cities by the end of 2020 is no longer practicable.”

He said ministers and councils “remain dedicated to introducing low-emission zones across Scotland’s four biggest cities to improve air quality and protect public health”.

Environmental group Friends of the Earth Scotland said the Covid-19 crisis has “highlighted our urgent need to reduce pollution”.

The group’s air pollution campaigner Gavin Thomson said: “There’s a strong evidence base on the links between air pollution and vulnerability to Covid-19. Pollution from traffic causes and exacerbates many of the heart and lung conditions that put people at heightened risk from the virus.”

Joseph Carter, head of Asthma UK and the British Lung Foundation Scotland, said he was “shocked and disappointed”, adding: “Recent research has demonstrated a link between the levels of urban air pollution and the effects of Covid-19, so it is vital now more than ever that we push ahead with LEZs to help protect our nation’s lung health.”