Gatwick Airport said it still has a "credible, privately-financed runway plan" after the government published new research suggesting it could provide greater economic benefits than Heathrow expansion.
The Department for Transport (DfT) released a series of fresh reports into the impact of building a third runway at Heathrow - its preferred option - as well as extending Heathrow's northern runway or expanding Gatwick.
It predicts that the total benefits to passengers and the wider economy would be worth up to £75.4 billion at Gatwick, compared with £74.2 billion at Heathrow.
This reverses an assessment by the independent Airports Commission, which backed a third runway at Heathrow in 2015 after concluding it would be more advantageous to the economy.
A consultation on the draft Airports National Policy Statement (NPS) - which sets out the Government's support for expanding the west London hub - initially closed in May, but has now been reopened until December 19.
A Gatwick spokesman said: "Gatwick welcomes the consultation on the revised draft Airports National Policy Statement which includes updated noise analysis and air traffic forecasts, and a new air quality plan.
"We will look carefully at this new consultation material which is long and detailed. We continue to offer a credible privately-financed runway plan to the Government."
Another DfT report warned that expanding Heathrow with either a third runway or an extended northern runway could contribute to the UK breaching EU air quality limits.
It stated: "Given the inherent uncertainties associated with air quality modelling, there remains a risk that the options could impact on compliance."
A second runway at Gatwick has a "low risk" of leading to the UK breaking pollution rules, according to the study.
New analysis also found that passenger demand is expected to exceed scenarios set out by the Airports Commission.
Extra capacity at an expanded Heathrow would be full after just three years according to the latest figures. This is seven years earlier than initially thought.
The DfT insisted it is "on track" to publish final proposals for expansion in the first half of 2018 for a vote in Parliament.
If the scheme is approved by MPs, Heathrow will submit a planning application and consult with local communities on detailed proposals.
The airport hopes to begin construction in early 2021, with the runway completed by the end of 2025.
Transport Secretary Chris Grayling said: "The case for expanding Heathrow is as strong as ever and we want to hear your views on it. This is an important consultation and I encourage everybody to get involved across the UK."
A Heathrow spokesman said: "The forecasts show expanding Heathrow, the UK's only hub airport, is even more important than previously realised.
"A third runway will ensure Britain's place in the world as an outward-looking trading nation. That's why the Government has committed to a final vote on expansion in the first half of 2018."