The Environmental Protection Department has refuted media reports the Polytechnic University has found that liquefied-petroleum gas taxis are more polluting than diesel ones.

The department today said the university's study supported that the replacement of diesel taxis by LPG ones has effectively alleviated urban street air pollution. It also showed that LPG taxis need proper maintenance as the vehicles get older.

The department said evidence shows that nitrogen oxides emitted by diesel taxis are up to 18 to 100 times more than those emitted by LPG taxis. Particulate emissions of LPG taxis are extremely low and their emissions of carbon monoxide and hydrocarbons are also lower than diesel taxis.

The department said one newspaper misquoted the study's findings, saying at a speed of 50kph LPG taxis would emit 0.07g of nitrogen monoxide per kilometre while diesel taxis would emit 0.05g. As confirmed by the university, the emission of nitrogen monoxide by diesel taxis was 0.18g per kilometre.

Reference only

Dr Chan Tat-leung, a key researcher of the study, said it did not consider particulate emissions. It focused on the use of roadside remote sensing technology to measure emissions of LPG vehicles and the effect of maintenance on such vehicles.

The emission data of diesel taxis was based on estimates derived from random samplings on the roadside conducted several years ago. There were differences in location, timing, road surface and driving conditions as compared with the current study.

Therefore, all the diesel vehicle emission data can only be used for reference and the LPG taxi emissions should also be further studied, he said.

Meanwhile, the department is working on a proposal to control emissions from petrol and LPG vehicles by using roadside sensors and chassis dynamometers to check emissions. A consultation on the idea will be launched in January.