LONDON (Reuters) - Heathrow Airport announced a public consultation on the proposed development of a third runway at Europe s biggest airport, saying it aimed to mitigate the environmental impact of expansion. Prime Minister Theresa May backed a $22 billion expansion of the London hub in October 2016, after decades of government indecision. But the plan has been controversial, with critics highlighting the possible impact on air quality in London and noise levels in the local community. Heathrow said it would seek the views of locals on the environmental impact of expansion and how the airspace around Heathrow is managed.  Over the past year, we ve been working hard to evolve our expansion plans and have come up with several new options to deliver it more responsibly and affordably,  said the airport s Executive Director for expansion Emma Gilthorpe.     The new discussions are separate from a previously announced government consultation on a National Policy Statement on airports, and is focused on the airport s plans for infrastructure and the impact on the local community. Transport secretary Chris Grayling has said that the government aims to give the go-ahead to the new runway in the first half of 2018. The latest consultation will launch on Jan. 17 and run for 10 weeks. 