A third runway at Heathrow would triple the number of early deaths from pollution linked to the airport, a new study claims.
In contrast, moving London's main airport to the Thames Estuary - a plan championed by London mayor Boris Johnson - would cut the number of deaths, the report by the Massachusetts Institute of Technology (MIT) and Cambridge University says.
They say a third runway at Heathrow would increase deaths from air pollution linked to the airport from the current 50 a year to 150 by 2030, with deaths more than doubling to 110 a year even if the extra runway is not built.
Nationwide, the number of deaths linked to aviation pollution at current capacity will rise from 110 annually today to 250 in 2030, the report says.
A third runway at Heathrow would add a further 10 deaths a year because of an expected reduction in pollution at other airports, which will lose flights to the new, expanded hub.
The scientists say that moving the UK's main airport to the Thames Estuary, the plan championed by the London mayor, could cut deaths by up to 70%.
The difference is explained by the south-westerly prevailing wind, which currently blows pollution north east from Heathrow into London, according to the report.
Pollution from a Thames Estuary airport would be carried out to sea.
Dr Steven Barrett from Massachusetts Institute of Technology explains more about the findings of his report and how he came to his conclusions:
Expanding Heathrow during the current parliament was ruled out in the coalition agreement in 2010.
The Government has appointed former Financial Services Authority chief Sir Howard Davies to lead an independent commission into airport capacity needs.
But his final report is not due until summer 2015 - after the next general election.
Boris Johnson repeated his call for a new "Boris Island" airport to the south-east of the city at the Conservative Party Conference last week, adding: "We are not taking the decisive action that we need to make ourselves competitive with other European countries, with Dubai, with all these competitors of ours that are putting on new runways."
A Heathrow spokesman said: "The issue of air pollution is one faced by all major cities across the world. Aviation is a far smaller contributor to air pollution than road traffic, however we are already taking significant steps to tackle the problem. For example, we subsidise local public transport so people can travel for free without the need for a car.
"We also charge airlines based on how green they are - so the cleanest aircraft are charged less to land at Heathrow."