Facing severe air pollution that is threatening the health of both people and the economy, the Hong Kong government yesterday announced a broad plan aimed at cutting automobile emissions by at least a third within two years. The package of regulations will, among other things, impose higher taxes on dirty diesel fuel and give grants to help taxi drivers buy vehicles that run on cleaner-burning liquid petroleum gas. Hong Kong Chief Executive Tung Chee-hwa pledged that the territory’s air would be as clean as New York’s or London’s in five years. Hong Kong’s business leaders have begun complaining in recent months that horrible air quality is driving off tourists and talented workers.