Gatwick's pleas to be expanded instead of Heathrow should be ignored, the chairman of the Airports Commission has urged the Government.
In July, Sir Howard Davies announced his recommendation that a third runway should be built at Heathrow to cope with the expansion in flights in future years.
He said that there were too many issue to overcome at Gatwick for it to be considered as a realistic option.
In a letter to Transport Secretary Patrick McLoughlin, Sir Howard claimed the impact on air quality of an expanded Heathrow would be "a manageable part" of the Government's efforts to meet EU limits for pollution in London.
He added: "Limited weight should be placed on the suggestion that air quality represents a significant obstacle to expansion."
Sir Howard defended the commission's findings on a number of other points such as cost, economic benefits and noise - and claimed some of Gatwick's arguments were "entirely misguided".
Gatwick chief executive Stewart Wingate criticised the letter and repeated his view that the Airports Commission was "flawed".
David Cameron has said the Government will make a decision on airport expansion by the end of the year.