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City Hall has declared a “high” air pollution alert for London after a hot spell and south\u2011easterly winds are expected to raise ground\u2011level ozone; the mayor urged behaviour changes to cut emissions while health bodies call for sustained policy action.<\/p>\n<\/div>\n
City Hall has issued a \u201chigh\u201d air pollution alert for London as a burst of hot, sunny weather is expected to push temperatures into the mid\u201130s Celsius and raise concentrations of ground\u2011level ozone across the capital. Forecasters at Imperial College London advised the mayor that south\u2011easterly winds could carry additional pollution from continental Europe, increasing ozone levels across the south\u2011east and prompting the warning to schools, boroughs and the public transport network.<\/p>\n
Ozone at ground level is a secondary pollutant: it forms when nitrogen oxides and volatile organic compounds react under sunlight and heat. According to the duty forecasters and international health agencies, elevated ozone can irritate and inflame the airways, reducing lung function and provoking coughing, chest tightness and shortness of breath; it can aggravate asthma and other chronic lung conditions and increase susceptibility to respiratory infections. Forecasters use these mechanisms, alongside meteorology, to determine when pollution poses an acute risk to public health.<\/p>\n
City Hall\u2019s alert carries practical public\u2011health advice. The Mayor of London urged Londoners to reduce activities that add to pollution and to look after the most vulnerable, noting that \u201cpollution and heat can be a dangerous combination.\u201d The mayor\u2019s office recommended choosing public transport, walking or cycling where possible, avoiding unnecessary car trips, switching off idling engines and refraining from burning wood or garden waste. City Hall says such measures both reduce immediate exposure and help limit the chemical precursors that form ozone.<\/p>\n
The warning sits against a broader public\u2011health backdrop. A Royal College of Physicians report has described modern air pollution as a national health crisis, linking long\u2011term exposure to thousands of deaths each year and substantial economic costs. The college\u2019s analysis highlights wide\u2011ranging harms \u2014 from cardiovascular disease to impacts on early life and cognition \u2014 and argues that the scale of the burden requires urgent, sustained policy action to reduce emissions and protect public health.<\/p>\n
London\u2019s alerting system has been developed and refined over the last decade: the mayor\u2019s office introduced public alerts in 2016 and Imperial College\u2019s Environmental Research Group has been the duty forecaster in recent years. Forecasts produced for the Mayor are combined with other public services such as airTEXT and the Met Office to create a single, city\u2011wide picture and to trigger displays on bus stop countdown signs, Underground screens and roadside boards when thresholds are reached.<\/p>\n
In February 2024 the Greater London Authority added a new, targeted channel for clinicians, sending direct notifications to GP practices and emergency departments so that healthcare professionals can prepare for high or very high pollution episodes. The GLA said the scheme is intended to help clinicians advise vulnerable patients and to reduce avoidable emergency admissions during extreme episodes of heat and pollution.<\/p>\n
Health agencies advise specific precautions for groups most at risk \u2014 children, older adults, people with existing lung or heart conditions and outdoor workers \u2014 including limiting strenuous outdoor activity when ozone levels are high and following individual medical plans for asthma or other respiratory disease. City Hall\u2019s messaging echoes these recommendations while framing short\u2011term protective actions as complementary to longer\u2011term measures to cut emissions.<\/p>\n
The alert underscores a persistent tension in public policy: short\u2011term warnings and individual protective advice can reduce immediate harm, but independent health bodies say only sustained emissions reductions will substantially lower the chronic burden of polluted air. City Hall points to measures it has introduced, including a major clean\u2011air charging zone, while calling for wider national and international action to tackle pollution that crosses borders and accumulates in warm weather.<\/p>\n