A green group is concerned that the projected air quality for a proposed third runway at Hong Kong's airport could be "manipulated" to stay within environmental objectives.
Friends of the Earth pointed out yesterday that projections for a third runway, given in an environmental impact report released last month, are less than the estimates given about five years ago for the adjacent Hong Kong-Zhuhai-Macau bridge project.
"We are worried that different assumptions can be adopted or even manipulated to avoid breaching the air quality objectives," Friends of the Earth assistant environmental affairs manager Melonie Chau Yuet-cheung said yesterday.
"If that's the case, it is a very dangerous move that will render the assessment useless," she said.
In the assessment for the bridge, carried out in 2008-09, nitrogen dioxide levels at Sha Lo Wan on North Lantau were projected to be 44 to 47 micrograms per cubic metre in 2031.
The bridge is currently under construction.
But in the runway assessment, conducted in the past two years and taking into account both projects, the level at the same location in the same year was projected to be 36 micrograms per cubic metre.
The bridge is linked to the eastern tip of the airport.
The group cited four other locations - including two schools and two residential blocks - in Tung Chung, where the air quality was projected to be better, taking into account both projects.
Chau said that while both projects used exactly the same modelling software to assess air quality, different assumptions yielded different results.
She said that apart from considering emissions from the project itself, the projection would also include emissions from nearby sources as well as regional air quality changes.
She suspected that the difference stemmed from the fact that the boundary crossing assumed regional air quality would flatten at 2015 levels, while the runway report assumed this would happen in 2020.
Chau said Guangdong's air quality now played a critical role in determining if a project in Hong Kong was likely to breach air quality objectives.
She also said that Lantau was already close to the air pollution limits and squeezing in more development would be impossible without breaching the pollution targets.
And she questioned whether the assessment should cover a recent proposal for a man-made island east of Lantau.
The Airport Authority has said its assessment was based on the most up-to-date data.
It said various factors had been considered, including the proposed emission reduction measures to be adopted by the airport, and cross-border emission reduction targets for 2020 set out in 2012.