The Mayor of London issued a high air pollution alert for Tuesday 10 November after forecasters warned that particle pollution could remain elevated following a foggy weekend.
City Hall said the alert followed advice from forecasters at Imperial College London. It urged people across the capital, particularly those most vulnerable to pollution, to look after themselves and take steps to reduce emissions.
Dense fog and very light winds had allowed pollution to build up over the weekend and linger into Monday morning, according to the mayor’s office. Smoke from Bonfire Night and Diwali fireworks, as well as wood burning, was likely to have contributed. The office did not give a breakdown of how much came from each source.
This was the fourth high air pollution alert issued in London in 2026. The previous high alert had been issued in June during a heatwave.
Warning shared with health services
City Hall said additional details had been shared with GPs and emergency departments so that health professionals had information to help vulnerable patients. Its alerts system also sends warnings to Londoners, schools and boroughs when moderate, high or very high pollution is forecast.
High alerts can be displayed in public places, including on bus stop countdown signs and across the Underground network. Direct alerts were sent to schools, councils and care homes between 5 and 8 November, before the Tuesday warning.
The alert is a forecast, rather than proof that the whole capital experienced the same pollution level. Available information indicated that actual levels were lower than expected, but did not specify a complete set of times and locations for those readings. Local measurements and forecasts can differ, and an alert for the city should not be treated as a confirmed reading for every neighbourhood.
London’s monitoring network includes reference stations providing hourly measurements and a network of lower-cost sensors. The city also uses diffusion tubes to assess longer-term nitrogen dioxide concentrations. These approaches provide different kinds of information; a monthly average is not the same thing as a reading at a particular hour.
What the health guidance says
The warning system uses thresholds based on the government’s Daily Air Quality Index. The index describes short-term pollution risk in bands ranging from low to very high. City Hall said the thresholds used for its alerts are above World Health Organization air quality guideline values and indicate levels at which short-term health effects may occur, particularly for people with existing conditions such as asthma or chronic obstructive pulmonary disease.
Government guidance says short-term exposure to air pollution can cause coughing, chest tightness, difficulty breathing or irritation of the eyes, nose and throat. It can also worsen symptoms for people with asthma, other lung conditions or heart conditions. Symptoms and individual sensitivity can vary.
For high and very high pollution, the guidance advises people to try to reduce their exposure, especially if they have symptoms. Adults and children with lung or heart conditions, and older people, are advised to adapt physically demanding outdoor activities, particularly if their symptoms worsen. Anyone with an agreed management plan should follow it.
The guidance also recommends speaking to a doctor or nurse about new symptoms, symptoms that get worse, or symptoms that do not improve after a week. For severe difficulty breathing, such as gasping or being unable to get words out, health guidance advises calling 999 or going to A&E immediately. The alert did not mean that everyone would experience symptoms.
Steps to reduce emissions
City Hall encouraged Londoners to walk, cycle or use public transport more often, and to avoid the busiest roads where possible. Drivers were asked to travel less where they could, share journeys, switch off engines when stationary and keep vehicles well maintained.
It also suggested composting garden waste or taking it to a refuse centre instead of burning it, and avoiding unnecessary use of wood burners or open fires. Those suggestions address sources of pollution; they are separate from the health guidance for people who may be particularly affected by poor air.
