I don’t think about what I’m breathing, but living in London I’m breathing filthy air. I can neither see nor smell the filth, but I’m now thinking about what I’m breathing after attending the Mayor of London’s conference on air quality last week. In a nutshell, air quality in London is poor, but showing some signs of improvement; yet the quality of the air is far better than in many of the world’s megacities, particularly cities like Dhaka and Delhi in South East Asia.

London’s Great Smog of December 1952, which lasted five days, killed 4000 in the immediate aftermath and up to 12 000 altogether. The lethal effect of the smog was not realised until undertakers ran out of coffins. The air was filled with sulphur particles and smelt of rotten eggs. I was living in London and nine months’ old. I remember subsequent smogs, and in my memory I wore a scarf that turned yellow around my mouth and could not see my hand in front of my eyes. More recently I’ve experienced similar smogs in Beijing and Delhi.

The London smogs of the 50s led to the Clean Air Act on 1956, which meant that if you flew into London you could actually see the city. But now the pollutants in the air—carbon monoxide, nitrogen dioxide, sulphur dioxide, ozone, and the particulate matter (PM10 and PM 2.5)—are invisible. Two million people, including 400 000 children, in London are living with illegal levels of air pollution, said Shirley Rodrigues, deputy mayor for environment and energy. The pollution causes some 9000 deaths a year—a similar number to those who died in the Great Smog of 1952, but these deaths are spread over time, space, and cause and not so visible.

I did, of course, know that London has high levels of air pollution (it’s often mentioned in the media), but I am typical in not paying much attention. This lack of attention and outrage is frustrating to those who campaign on air pollution, who reflect on how adulteration of food or water causes much greater concern.

Although air pollution may be bad in London, it is much worse in many places, particularly Africa and South Asia. Air pollution in Britain accounts for 560 DALYs [disability adjusted life years] per 100 000 people each year compared with 2550 for India and 4045 for Nigeria. WHO estimates that nine of 10 people in the world breathe air that exceeds WHO limits, causing eight million deaths a year—4.2 million from outdoor pollution and 3.8 million from indoor pollution.

Back in the 50s when Austin Bradford Hill and Richard Doll were searching for the cause of the epidemic of lung cancer their favoured hypothesis of the cause was traffic pollution. They were right, but at that time smoking was the major cause, but now smoking has declined. Air pollution does cause lung cancer, but it also contributes to chronic obstructive pulmonary disease (COPD), asthma, respiratory infections, heart disease, stroke, dementia, impaired child development, and low birth weight and prematurity in the newborn. Research continues to show new connections with disease.

Air pollution and the climate emergency share the same causes, and the 2015 Paris Agreement within the United Nations Framework Convention on Climate Change includes a commitment to clean air for everybody by 2030. Christiana Figueres, executive secretary of the UN Framework Convention on Climate Change, has called it “the most important health agreement ever,” and 195 countries have signed it, although President Trump has pulled the US out of the agreement. The agreement requires countries to do better every five years, and next UN climate change summit (known as COP26) will be held in Glasgow next year. Maria Neira, the head of air pollution for WHO, said that COP26 should be a “health COP.” “Health,” she said, “can be the motivator, the engine for tackling air pollution and the climate emergency.”

Outdoor air pollution is worse in cities, and C40 Cities Climate Leadership Group (C40) is a group of global cities working to combat the climate emergency and air pollution. Started by Ken Livingstone, who was then London mayor, in 2005, C40 now confusingly includes 94 cities, half of them in low and middle income countries. The cities contain around a twelfth of the world’s population and account for a quarter of the global economy. More than half the world’s population now live in cities, and politically they become increasingly important not least because they find it easier to reach agreement than nations—think of London voting 60% against Brexit.

The cities learn from each other and compete to be top of the class. The London Mayor Sadiq Khan has put combatting air pollution at the centre of his commitments, and one initiative that has interested other cities is the ultra low emission zone (ULEZ). Begun in April this year it means that all but very clean cars and vans must pay £12.50 to enter the zone, which covers the centre of London. An initial evaluation, said Rodrigues, shows that nitrogen dioxide has declined by 29%. Carbon dioxide emissions from transport have also declined by 4%. The proposal is to extend the zone in 2021. There are also many other initiatives, including increasing electric buses and charging points for electric cars, said Rodrigues. But the main aim must be to reduce car use and increase the number of people walking, cycling, and using public transport.

Rodrigues also made clear that London will not be able to achieve WHO limits on air pollution without the city being given more powers by the government —for example, over construction. Indeed, national progress will be necessary for London to achieve the limits.

The UK Health Alliance on Climate Change (of which I have just become he chair) was prominent at the meeting with Nicky Philpott, the director, leading a session, and a film that the Alliance has made being shown. The film featured Andrew Goddard (known to all as Bod), the president of the Royal College of Physicians, cycling through London with an air quality monitor on his bike and interviewing various people, including Wendy Burn, the president of the Royal College of Psychiatrists, about the health effects of air pollution. His trip ended with an interview with Rodrigues at City Hall. The film is online here.

Richard Smith was the editor of The BMJ until 2004.

Competing interest: RS is the unpaid chair of the UK Health Alliance on Climate Change, and he cycled behind Bod with a camera strapped to his chest to make the film. The BMA and the BMJ are members of the Alliance, and the two employees of the Alliance are based in the BMJ offices.