April 18, China’s southern harbor city of Hong Kong has jumped to third place in an index of Asia’s most liveable city for expatriates, up two places from a year earlier, despite no improvement in its infamously dirty air.

The index, produced by ECA International, a human resources consulting company, assessed 49 Asian cities and 263 cities worldwide to include factors such as climate, infrastructure, political tensions and air quality. Singapore came top regionally and globally.

"Hong Kong's rise up the ranking is a reflection of Tokyo's and Yokohama's fall rather than any locally generated improvements in Hong Kong's score," said Lee Quane, Asia regional director for ECA International.

Tokyo and Yokohama ranked higher than Hong Kong in 2011, No. 3 and No 4, respectively, but last year’s deadly earthquake and tsunami and the aftermath of a radiation leakage in the nearby No.1 Fukushima nuclear station pushed both down one place in this year’s index.

Hong Kong’s score was reduced by its poor air quality, the third worst score for any Asian city other than Beijing and New Delhi and among the worst locations worldwide, the survey said.

A local think tank, Civic Exchange, blamed aging buses and trucks on Hong Kong’s streets as the key cause of air pollution, which results in more than 3,000 premature deaths in the financial center each year. The situation is so bad that some expats are considering relocating to rival regional centres, threatening the city’s ability to attract top talent and remain a leading global financial hub.

“I am leaving Hong Kong explicitly because of the air,” Alex Turnbull, an Australian banker at a Wall Street firm, who plans a move to Singapore in May, told Bloomberg in March. “Hong Kong is at risk of being irrelevant in the long run.”

But for those looking to set up an office to do business with the world’s second-largest economy, Hong Kong still remains the best choice among all the big cities on the mainland.

Shanghai, ranked 12th locally and 83rd globally (Hong Kong ranked 11th worldwide), is the most livable city in mainland China, followed by Beijing, where the problem with air pollution is much more severe than in Hong Kong.

Air pollution in China’s capital reached “hazardous” levels several times last winter, as rated by the U.S. embassy in Beijing, which produces its own pollution readings using a different gauge to Chinese authorities and broadcasts them online and on Twitter, according to AFP.