1993: A Hong Kong University study finds half of the nitrogen oxide and a third of RSPs (respirable suspended particulates) in the SAR are from trucks travelling to the mainland, and suggests restrictions be imposed.
1994: An Environmental Protection Department (EPD) study finds most air pollution is caused by 'light vehicles', such as taxis and public light buses, and commences drafting a bill to make all vehicles under four tonnes change from diesel to petrol.
1995: After lobbying from transport industry, the Democrats, the Democratic Alliance for the Betterment of Hong Kong and the Liberals vote against the diesel-to-petrol bill in Legco. and ask for further research.
1998: Chronic respiratory diseases and asthma levels climb, smog becomes common. The EPD introduces a year-long liquefied petroleum gas (LPG) trial for 30 taxis. After the trial there will be further reports and meetings and consultancy before legislation is drafted.
2004: Legislation to convert all taxis to LPG is finally implemented, reckons Christine Loh Kung-wai, legislator and chairman of Legco's Environmental Panel. If she's right, it will have been more than decade in the making.