By World Health Organization standards, Hong Kong's air is so polluted it is only safe to breathe 41 days a year. Cars and power stations, as well as factories in southern China, are blamed for the haze.
But scientists say ships also damage the air in this city, home to one of the world's busiest ports. Marine transportation is now responsible for almost 10 percent of the pollution. C.M. Wong, a public health expert at the University of Hong Kong, has been studying local air quality for nearly 20 years.
"Hong Kong is an important port," said C.M. Wong. "Marine traffic becomes a very major part of air pollution in Hong Kong. They burn things called residual oil or bunker fuel oil. This fuel has a very high sulfur content. The problem is growing."
Sulfur dioxide, says Dr. Wong, is a significant cause of heart and lung disease. His team estimates that sulfur dioxide, along with ozone, nitrogen dioxide and particulate matter, cost Hong Kong $2.2 billion a year in hospitalization costs and lost productivity. In 2010, they say, air pollution has already caused 480 premature deaths.
But one vessel might kick-start the effort to clean up Hong Kong's sea air - the sleek blue and yellow catamaran, the Solar Golf.
The 100-seat boat recently began operating as the world's first commercial hybrid ferry service, here in this island-dotted territory. It runs between Hong Kong Island and a public golf course on Kau Sai Chau Island.
It will soon be joined by three sister ships, one of which is equipped as a floating classroom to teach children more about renewable energy.
"The vessels have hybrid solar-power electrical and diesel engines, which can operate in parallel to save up to 50 percent in fuel consumption and about HK$2.5 million (US$320,000) a year in operating costs in comparison with the existing ferries," said Gillian Leung, the golf course spokeswoman. "Lightweight materials in the hull help save energy and the solar panels will last at least 15 years."
The captain, Leung Kam-yiu, gives a pre-departure briefing and he's very excited because today is the first time he has taken sole command of the Solar Golf.
He also explained more about how the parallel engine system works: out at sea the ferry uses low-sulfur diesel fuel, and in coastal waters, the crew switches to the solar-charged electric "E" motor to minimize on-shore noise and air pollution.
The new ferries are by no means Kau Sai Chau's only green initiative. All 205 golf carts on the course have also been converted to solar power.
Combined, Leung estimates the new ferries and golf carts will reduce carbon dioxide emissions by 1,280 tons a year - the equivalent annual absorption of 188,000 mature pine trees.
Prentice Koo of Hong Kong Greenpeace thinks that, although comparatively small, Kau Sai Chau's efforts are important because the government response to the renewable energy debate has been weak.
"The government only has a policy recommendation to achieve one to two percent renewable energy by 2012," said Koo. "It's very low target compared with China."
He says the government needs to do better. The investment, Koo says, is in the well-being of future generations.