In 1998, the Beijing government recognized that its air pollution had resulted in severe environmental degradation, and it implemented a project to introduce alternative low-emission fuel vehicles. Because the emissions from transit buses and taxis accounted for a large share in total vehicle emissions, the government decided that the first alternative fuel vehicles (AFVs) developed should be buses and taxis.

In September 1999, the first CNG (compressed natural gas) transit bus appeared in Beijing, marking the beginning of the project. By the end of 2001, the city had 1,630 NGVs (natural gas vehicles), the most of any city in the world. In addition, 3,000 buses were modified to become LPG (liquefied petroleum gas) buses (bi-fuel). By the end of 2001, more than 30,000 taxis had been modified to become bi-fuel cars (using taxi-LPG-gasoline). To achieve its targets, the authorities focused on the construction of CNG and LPG stations, the development of single fuel (LPG) vehicles, mainly taxis, and the development of new CNG buses.

Of all the liquid or gaseous fuels ready for commercial transportation use, CNG offers the greatest reduction in emissions compared to gasoline, as illustrated by the results of Beijing’s initiative below.

• Carbon dioxide emissions from CNG were approximately 19 per cent less, while producing the same calorific value;
• Carbon monoxide using CNG was reduced by 65 to 90 per cent;
• CNG resulted in a reduction in non-methane hydrocarbons (NMHC) of up to 97 per cent;
• Particulates were virtually eliminated; and
• Ozone reactivity from NGVs was up to 80 to 90 per cent better than that from gasoline emissions.

A study of NOx and CO concentration was carried out in 2001 for Beijing. Although the total number of vehicles in the city had increased rapidly in the three years since the programme began, the concentration of NOx and CO had not correspondingly increased. In fact, their concentration dropped by 16.4 per cent and 21.2 per cent, respectively, in three years.

For cities with a plentiful supply of natural gas, NGVs, when compared with gasoline vehicles, are a good choice to reduce emissions of NOx, CO and PM. However, CH4 emissions from NGVs are higher when compared with that of conventional vehicles, and CO2 emissions from NGVs are also greater than that of efficient diesel vehicles. Other shortcomings of NGVs include high initial costs, heavy weight, short range and safety problems. Bi-fuel vehicles may not be as environmentally efficient as anticipated due to poor quality of LPG, low efficiency caused by two fuelling systems and relatively high operational costs.

Case study courtesy of the UNEP Publication, Reducing Emissions from Private Cars: Incentive measures for behavioural change.