In London, high-pollution days caused an extra 87 cardiac arrests on average, an extra 144 strokes, and 74 children and 33 adults ending up in hospital with asthma-related issues.
Birmingham saw 12 more out-of-hospital cardiac arrests, 27 additional admissions for stroke and 26 more for asthma.
Bristol, Liverpool, Manchester, Nottingham, Oxford and Southampton saw between two and six more out-of-hospital heart attacks and up to 14 extra hospital admissions for both stroke and asthma on high-pollution days.
Only in Derby was there no apparent increase.
‘Avoidable deaths’
Among the long-term risks associated with high pollution levels are stunted lung growth and low birth weight.
The King’s College research also suggests cutting air pollution by a fifth would decrease incidents of lung cancer by between 5% and 7% across the nine cities surveyed.
Mr Stevens said: “It’s clear that the climate emergency is in fact also a health emergency.
“Since these avoidable deaths are happening now – not in 2025 or 2050 – together we need to act now.”
The figures were published ahead of Wednesday’s International Clean Air Summit hosted by Mayor of London Sadiq Khan and the UK100 network of local government leaders.
UK100 director Polly Billington said: “Local government needs additional powers and resources to address this public health crisis.”
The Department for Environment, Food and Rural Affairs said it was “taking urgent action to improve air quality and tackle pollution” and that new legislation will “increase local powers to address key sources of air pollution”.
“We are already working hard to reduce transport emissions and are investing £3.5 billion to clean up our air.”