A third runway at Heathrow would lead to significantly more early deaths from pollution than a new airport built in the Thames Estuary, a study has warned.
The research, funded by US university MIT, suggests Heathrow aviation pollution causes about 50 early deaths a year and this number is rising.
That figure may climb to 150 if a third runway is built, the study claims.
If Heathrow closed and an airport was built in the Thames Estuary, there would be 50 deaths annually, it said.
The report's lead author, Steve Barrett from MIT, said early deaths would be reduced by more than 60% if an estuary airport was built because weather conditions would expose fewer people to pollution.
He told the BBC: "Because of the location of the [Thames estuary] airport, such an airport would be further away from major population centres so fewer people would be exposed to pollution from that airport.
"Another important factor is the winds in London are south-westerly, so towards the north-east, so pollution from Heathrow gets blown over London.
"If you instead had an airport in the Thames Estuary, that pollution would get blown over the English Channel and North Sea," he added.
Currently about 110 people in the UK die early every year "due to airport emissions". Of these deaths, about 50 are directly due to emissions from Heathrow, the report said.
By 2030, without airport expansion, the number of early deaths from airport emissions across the UK is projected to more than double to 250. Of those, 110 could be from Heathrow, the report continues.
If a third runway was built, the study - written in collaboration with Cambridge University - warns that the estimated figures for Heathrow could rise from 110 to 150.
Aviation experts say the study does not give the full picture because passengers would need to travel to a more remote airport, and that could also cause pollution.
Ministers insist any decision on airport expansion will take account of environmental and social impacts.
Nic Ferriday, from campaign group AirportWatch, told the BBC: "The study does match up quite well with a study that was actually done for the Greater London Authority that showed 4,000 people per year dying from air pollution.
"Those are very large figures. That sort of death toll ought to be a really significant issue for this government."
Last month, the government appointed former executive chairman of the Financial Services Authority, Sir Howard Davies to lead a review into how the UK might expand its airport capacity in the South East, amid suggestions the prime minister would perform a U-turn on his pledge not to build a third runway at Heathrow.
London Mayor Boris Johnson, meanwhile, has backed the concept of a Thames island airport, with one of three plans unveiled dubbed "Boris Island".
A spokeswoman for the mayor's office said his team were "keen to examine" this latest research.
She added: "There are clear environmental benefits from meeting the increasing demand for aviation at a hub airport located to the east of London, rather than the madness of expanding an airport that is already constrained by location, straining at the seams and in the heart of the western suburbs of London."
A Department for Transport spokesman said: "Maintaining the UK's status as a leading aviation hub is vital to our economy.
"This is why we have set up an independent commission to look at all the options, which will naturally include an assessment of the environmental and social impacts of any proposal."
Some financial analysts say the Thames Estuary project would only be financially viable if Heathrow was closed down.
A spokesperson from Heathrow said airport owners BAA are already taking "significant steps" to deal with air pollution.
"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," the spokesperson added.