Municipal governments all over the world, particularly in developing countries with rapidly growing fleets of cars and choking air pollution, have been rushing over the last few years to force taxis and buses to switch to burning liquefied petroleum gas and compressed natural gas, frequently offering subsidies for them to do so.
But one of the early leaders of the trend, Hong Kong, said on Friday that the city’s shift over the last decade to almost complete dependence on LPG for light commercial vehicles had produced unintended consequences. Concentrations of nitrogen dioxide, one of the most important contributors to smog, surged by a fifth in Hong Kong’s air from 2008 to 2012, and a team of local and international scientists have traced the cause to LPG-fueled vehicles, Hong Kong environmental regulators said at a news conference.
The problem lies in the taxis’ and minibuses’ catalytic converters, said Christine Loh, the under secretary for the environment. Unless replaced every 18 months for cars and light buses that are driven
nearly around the clock, the catalytic converters become fouled, and the vehicles begin emitting extremely high levels of pollution.
“The LPG vehicles, which are supposed to be cleaner, are spewing out very high levels of nitrogen,” she said. Although natural-gas-powered vehicles have not been deployed
on a large scale in Hong Kong, they would pose the same problems, she added.
As a result, the Hong Kong government in the coming months will pay for the free replacement of catalytic converters on the city’s entire privately owned fleet of roughly 18,000 taxis and several thousand minibuses, Ms. Loh said. Pang Sik-wing, the city’s principal environmental protection officer for air sciences, said that the replacement effort would cost about 10,000 Hong Kong dollars, or $1,290 per vehicle.
After the first free replacement, taxi and minibus owners will be responsible for replacing catalytic converters every year and a half at their own expense. Hong Kong will deploy five mobile sensor systems next year to measure the pollution from passing vehicles and send automatic notices to the registered owners of any vehicle surpassing emissions standards, requiring them to take in their vehicles for repairs or risk losing their vehicle licenses.
“We will strictly enforce the emissions standard,” Mr. Pang said at a news conference on Friday morning with Ms. Loh.
The initiative comes as large areas of northeastern China struggled a week ago with smog so thick that schools closed and motorists had to slow down to drive through the murky air. While that smog has been linked overwhelmingly to coal consumption, vehicles have also played a role, particularly diesel-burning heavy trucks.
Cities across China have been seeking to mitigate the problem by rapidly converting taxi fleets to LPG or CNG — taxis sometimes have to wait as long as an hour to refuel because service stations with the necessary fuels have not been built fast enough. Ms. Loh said that the Hong Kong government had alerted Beijing to the catalytic converter maintenance difficulties encountered here, and officials are working to come up with solutions there.
Wong Pokeung, the chairman of the Hong Kong Taxi Owners Association, said in a separate telephone interview that the city’s taxi owners welcomed the free catalytic converters but would have replaced the emissions control equipment even without government assistance. Cars with up-to-date emissions equipment produce less black smoke, have more power and achieve better fuel efficiency, he said.
After the Hong Kong government offered subsidies of as much as 40,000 Hong Kong dollars, or $5,160, a decade ago for conversions to LPG, all but one of Hong Kong’s 18,138 taxis now burn LPG, Mr. Wong said. The owner of a single taxi has insisted on using diesel but has kept his reasons to himself, Mr. Wong added.
The city’s minibuses have also converted to LPG, for which local taxes per gallon are much cheaper than for other fuels.
Larger buses in Hong Kong continue to use diesel, including the picturesque double-decker buses that have been a staple of mass transit here since before Britain returned the territory to China in 1997. Franchised bus operators have long resisted switching, arguing that only diesel engines can push buses up Hong Kong’s steep hills while still providing enough power for the robust air-conditioning systems needed to ward off the sweltering heat during late spring, summer and early autumn.
The Hong Kong government is preparing to submit a bill to the legislature that would set deadlines for the retirement of all older diesel-powered vehicles that do not meet modern emissions standards and whose compliance has been grandfathered until now, Ms. Loh said. The bill will set “death dates for each of these categories — this is not a voluntary scheme, this is a mandatory scheme.”
Air pollution tends to be less severe in Hong Kong than in northern Chinese cities but still much worse than in the United States or in the European Union. Much of the pollution in Hong Kong is generated by factories just across the border in mainland China, as the city’s seven million people are part of an “air shed” of more than 50 million people covering a sizable area of the Pearl River Delta, Ms. Loh said.
Referring to air quality standards set by the World Health Organization in Geneva, she added that, “Hong Kong could shut off tomorrow, we would still not meet W.H.O. standards because there are emissions from our neighborhood.”