Heathrow airport can be built without breaking European pollution laws, a new study has found.
The independent study, led by the University of Cambridge and seen by The BBC, said the general pollution level will drop below “the critical level” because increased pollution from the runway will be counteracted by reduced pollution from the wider area.
The study, which has no formal links to an airport or government, measured poisonous nitrogen dioxide (NO2) levels using sensors in and around Heathrow.
Prof Rod Jones from the University of Cambridge told the BBC: "If there is the development of a third runway, we expect there to be a marginal increase in NO2 coming from the airport itself, but that would be against the background of reduced NO2 from other traffic, because of Euro 6 engines and electrification of the traffic fleet."
The study used 40 sensors to measure which emissions had been “blown in” the area, mostly from central London. That allowed researchers to separate emissions that were “associated with airport activities” from background pollution, and meant they could predict what would happen in the future.
“The pollution that we are seeing at Heathrow and around Heathrow is not all coming from the airport or airport activities,” Prof Jones told the BBC. “It’s coming from the wider transport in the London area.
“You can separate the emissions which are not associated with airport activities from those which are, so not all of it is coming from the airport.
“The issue here is that the background pollution, which is not necessarily associated directly with the airport itself, is likely to reduce largely as the traffic fleet changes over the next decade.”
It is understood a decision on whether to approve a runway at Heathrow or Gatwick is to be made later this month.