Last Sunday evening, the air over London achieved a remarkable quality. As winds died and a freezing stillness gripped the city, levels of nitrogen oxides and particles of soot slowly built up in the air until they reached maximum measurable levels at 24 different locations across the capital. It was a degree of pollution that had never been recorded in London since the government introduced its current methods and scales for recording air quality, the Daily Air Quality Index, in 2012.

“What we recorded was a very intense pollution event over London – in common with several other areas of western Europe,” said air pollution expert Gary Fuller, of King’s College London. “We had not seen anything like it here for the past five years.”

When level 10 degree of pollution is reached, men, women and children with lung problems, adults with heart conditions, and older people are all advised to avoid strenuous physical activity, while asthma sufferers are told to use their reliever inhaler more often. This was the grim scenario that was repeated at 24 locations across the city, from Swiss Cottage to Mitcham and from Teddington to Dagenham.

But what was striking was not just the extent and severity of pollution but its timing. Sunday night is a period when the city’s normally hectic traffic reaches its lowest ebb. People stay at home to watch television or wander to the pub. Generally, they leave their cars untouched.

Yet, the optical and mass spectrometers used by Fuller and his team indicated that levels of pollution that are normally linked to vehicle emissions had reached an unprecedented high. How could low traffic volumes be associated with air pollution that is usually linked to revving cars and motorbikes?

Fuller believes several factors were involved – though his instruments indicate the involvement of one quite specific phenomenon that recently emerged as a villain threatening the air we breathe: the wood-burning stove.

“One clear factor we could see through our measurements was that high levels of pollution were coming from wood-burning stoves,” he said. “They produce particulates that have a distinctive colour and spectroscopic signature that we can pick up very accurately in our machines. And of course, a cold weekend evening is the time when most people with wood-burning stoves like to sit in front of them to keep themselves nice and cosy. We could see that in the impact they had on the air of London last Sunday.”

The emergence of wood-burning stoves as an environmental villain – not just in London but across the nation – has produced a spate of headlines suggesting their growing use is likely to trigger the return of “pea-soup” fogs, which will kill of tens of thousands of individuals, with children and the elderly on the front line.

However, this is an extreme scenario and few scientists believe it is likely to materialise in the near future even at the present rate of the stoves’ growing popularity. An illustration is provided by studies by Fuller and others. These have shown that the monthly contribution of wood-burning stoves to particulate levels in the air varies from a maximum of around 10% in January down to 2% in August. But these figures are several years old and it is not clear by how much the use of stoves is increasing. Nevertheless, from this baseline it is clear that wood-burning would have to rise by a vast amount to bring back pea-soup fogs to London.

Even so, the wood stove controversy reveals the growing fears that many have about changes that affect the air we breath. Many believe its quality is being compromised and is declining. But is this true? Is the atmosphere changing dangerously and if so, what do we need to do to stop this?

A look at last week’s pollution provides some clues – other factors were involved in London’s atmospheric woes this winter. One couldn’t be more simple: the weather. “Meteorological conditions have been stagnant for several weeks,” said Martyn Chipperfield, professor of atmospheric chemistry at Leeds University. “There has been a stable, blocking anticyclone resting over Britain and that has trapped air over the country. There has been nothing to blow the pollution away. Worse, any winds that we have had have come from the south east, from Europe where the air is already polluted. Our prevailing winds usually blow in from the Atlantic bringing in fairly fresh air. Instead, all we have had is the odd puff of already polluted air.”

In addition, there is the particular geography of London, which leaves it badly exposed to fogs and pollution. The city nestles in land that is surrounded by hills and air gets trapped in this basin, particularly when wind flow is low and temperature inversions occur. Add to this, the high levels of vehicle use in its thoroughfares and you have a recipe for grim pollution.

An illustration is provided by the district of Brixton in south London. A major north-south thoroughfare runs past its houses and bars and restaurants. Brixton is also relatively low-lying – to the detriment of its air quality. According to last week’s Brixton Bugle, pollution on Brixton Road exceeded World Health Organisation guidelines for exposure to nitrogen oxides on 21 occasions on just one day this year, 5 January. The district has the worst air pollution in London, it is claimed by campaigners – with some urging that outdoor food and drink sales be stopped when air pollution levels are at their worst. As mayor Sadiq Khan has put it: “Everyone – from the most vulnerable to the physically fit – may need to take precautions to protect themselves from the filthy air.”

London’s problems have led civic leaders to advocate a host of anti-pollution measures, the latest being plans to change parking regulations to make it more expensive for owners of cars with diesel engines to park in the city. (Almost half the city’s nitrogen oxide pollution comes from diesel vehicles, it is claimed.) It remains to be seen how effective such measures will be.

The Department for Environment, Food and Rural Affairs has fixed the year 2025 as the date London has to meet EU air-quality standards. King’s College London’s researchers suggest that 2030 is a more likely date. That is a long time to wait before the city gets its environmental act in order.

However, it should be noted that, compared to many other cities, London’s pollution problems are mild. Three months ago, Delhi was swathed in a thick carpet of fog that persisted for weeks and which is believed to have been triggered – at least in part – by the setting-off of fireworks during India’s Diwali celebrations in October.

Last week, officials in Beijing urged residents to refrain from setting off fireworks for the Lunar new year celebrations. This follows the decision by Henan province to ban the practice to limit the heavy pollution that now blankets so much of China. By those standards, London’s problems are mild.

For good measure, it should also be noted that both nitrogen oxide emissions and particulate emissions have declined steadily from 1990 to 2014, the most recent year for which figures are available. Improvements in diesel engine technology have made a difference though confidence in statistics in this area has been dented by the VW emission scandals – in which the company was revealed to have deceived regulators about the real level of nitrogen oxide emissions from its cars.

“The particular concern we have today are the oxides of nitrogen that are generated - in power stations and in cars and other petrol-burning vehicles,” said Chipperfield. “It is not clear if climate change will lead to the arrival in Britain of more of the blocking anticyclones that have caused so many of our recent problems. Last year our weather problems were caused by storms, after all. On the other hand, this sort of thing is not going to disappear.”

Campaign groups have claimed that thousands of people die every year because of elevated levels of particulates and nitrogen oxides in our atmosphere. Yet nitrogen oxides are not particularly dangerous and can be given in fairly high doses to men and women without serious effects, said Anthony Frew, professor of allergy and respiratory medicine, at the Royal Sussex County Hospital.

“We have done experiments in which healthy people inhaled air in which nitrogen oxides were at levels that were far higher than those you get in polluted cities and found that it does not do anything,” said Frew. “However, for people with asthma and other conditions like that, it is harmful.”

Nitrogen oxides are also believed to affect white blood cells and prevent them operating at maximum efficiency, thus leaving them more likely to succumb to certain infectious diseases. In addition, it has been found that soot particles in the atmosphere are linked to cardiac disease.

What causes the real controversy is the manner in which health statistics have been used to bolster the notion that air pollution is deadly. One example is the the use of the statistic that in 2008, around 40,000 early deaths were caused by nitrogen oxides and particulates in the atmosphere in Britain. Over time, this figure has been misused to suggest that 40,000 deaths – as opposed to early deaths – were linked to air pollution. That simply is not true, said Frew. “It is untrue to say that 40,000 people died from air pollution. What is happening is that a lot of people are dying slightly sooner than they would if there was no air pollution.”

In addition, the concept of early death is vague, he added. “One teenager killed at the age of 17 represents an average of about 70 life years lost. Equally, 840 people losing one month at the end of their lives is also 70 life years lost but society would usually put more value on the life lost at 17 than the 840 slightly shortened lives, even though the life-years lost are the same.”

However, it is the latter statistic that is the most realistic version of what is happening. This is no excuse for inaction, argue scientists like Frew. Britain needs to reduce its nitrogen oxides and particulates levels to agreed EU limits and to a tight timetable. But this needs to be done calmly, with a sense of perspective.