The Thames is wreathed in smog—the Mayor of London, Sadiq Khan, issues an air quality alert and announces a new system of air quality warnings. There will be road-side dot matrix message signs on the busiest main roads into London, with instructions to switch engines off when stationary to reduce emissions. Air quality messages will be displayed on countdown signs at bus stops and river pier signs across the city as well as electronic update signs in the entrances of all 270 London Underground stations. Down the line from the studio the breakfast TV interviewer asks “what’s the point of the warnings, what can anyone do?” We have no choice but to breathe the air that’s there, so on the face of it this is not an unreasonable question. In fact there are three important constituencies these warnings are addressed to.

The first target is politicians and the political process—externalities, uncounted costs, are a cause of market failure. It is vital to raise the political cost of ignoring air quality. The Government is in breach of air quality regulations, with the British Lung Foundation reporting that 3,000 schools have been identified across the UK in areas of illegally high pollution. A public aware of air pollution and the harm it is causing to them and their children is an important step towards action to address the problem. Politicians respond to public pressure. Make an appointment. Talk to your MP about it.

The second target is people as polluters. Pausing on the way to the interview that morning I counted 100 consecutive cars crossing Lambeth Bridge—84 were occupied by a single driver only. Some may feel they have no alternative, but for many there is a choice to use public transport or walk or cycle. You’re not stuck in the traffic, you are the traffic.

The third target is the vulnerable. People with lung disease and other long term conditions can take some steps to reduce their exposure. At the worst times, staying indoors and avoiding strenuous exercise may be necessary. Avoiding busy roads is sensible. Approaches to map pollution hot spots, such as the Cleanspace app, may help with this. Pollution increases the risk of exacerbations in people with COPD and asthma. They should be prompted to watch out for any increase in symptoms and to make sure that they know what to do if they develop a flare up—check their self-management plan or rescue pack.

Air pollution causes about 40,000 deaths per year in the UK according to a recent report from the Royal College of Physicians. WHO figures show that, worldwide, ambient air pollution contributes to 5.4% of all deaths. Reducing air pollution and the harms it causes is a personal and political issue—an informed public is a vital first step.

Nicholas S Hopkinson is a reader in respiratory medicine at Imperial College, London.