HONG KONG ~ Hong Kong’s air pollution passed the danger level again this week, reigniting concerns about public health and fears that the choking smog could hamper tourism and investment.

Some of the world’s tallest skyscrapers were virtually invisible in the murk despite a series of measures to try to fight what is rapidly becoming Hong Kong’s top social and political problem.

Across the southern Chinese territory, the Air Pollution Index on Monday passed the critical 100 mark, the point at which those with respiratory or heart problems are urged to stay home.