Expansion plans for Heathrow Airport have divided MPs
A third runway at Heathrow will be a "white elephant" unless aviation is made greener, a think tank has said.
The Institute of Public Policy Research said if the runway is approved, conditions for meeting noise and emissions targets must be attached.
After months of speculation, the prime minister is expected to rubber stamp the controversial plans this week.
A Sunday newspaper claims London Mayor Boris Johnson will lead a legal challenge if the scheme is agreed.
The Sunday Times says a report prepared for the Conservative mayor has concluded the proposed runway at the west London airport would put the health of Londoners at risk and blight communities under the flight path.
Mr Johnson has previously put forward the idea of a new 24-hour airport on an artificial island in the Thames Estuary, which could possibly replace Heathrow altogether.
The Conservatives and Lib Dems oppose the idea of a new runway, as do environmental groups, while some backbench Labour MPs are calling for a rethink.
The Institute of Public Policy Research (IPPR) think tank said the government should not commit to a third runway unless the aviation industry's own emissions targets were guaranteed for any aircraft which wanted to use the new runway.
The targets include cutting carbon dioxide emissions and noise in new aircraft by 50% and nitrogen oxides by 80% by 2020.
The Institute's climate change head, Simon Retallack, said: "If a third runway is built without these conditions attached, European air quality standards will continue to be breached, noise pollution for households on flight paths will increase and a valuable opportunity will be missed to ensure the aviation industry prepares for a low carbon future.
"[Heathrow operator] BAA and the airline industry must bear the risk that a third runway will be a white elephant if aviation cannot be made greener."
BAA and its main customer British Airways say the short runway is vital if the airport is to stay competitive.
The government had been due to make a decision about Heathrow before Christmas, but the date was put back to January by Transport Secretary Geoff Hoon.
An announcement on the plan is tipped for the middle of this week, as long as it is approved by the cabinet on Tuesday.
More than 50 Labour MPs are opposed to the proposal and Environment Secretary Hilary Benn has voiced reservations about the impact of the development.
A Department for Transport spokeswoman said a date had not been set for an announcement and "neither has a decision been made".