New eco-friendly buses may not be able to help clear the air as expected because a key emission-reducing fluid used by Euro IV engines is available at only a few petrol stations.
Public Omnibus Operators' Association chairman Yeung Wai-hung said most Euro IV-compliant buses required the use of AdBlue, a urea solution which can cut emissions. But it is only available in 16 petrol stations and eight vehicle dealers' offices.
Mr Yeung said the industry was reluctant to make the switch: 'If only a few petrol stations offer urea and there are no backup measures from the government, how can we be convinced to join the scheme?'
Twelve models of Euro IV commercial vehicles, mostly large passenger buses, require the use of AdBlue, usually at one part to 20 parts of diesel. Shell and Caltex, which do not sell AdBlue, said they were studying the possibility of carrying it. All Euro V vehicles would require it.
Lo Kok-keung, of Hong Kong Polytechnic University's department of mechanical engineering, said urea was an emission-cutting chemical.
'If Euro IV heavy vehicles run without urea, it won't cut the nitrogen emissions effectively. So there will be no difference between Euro III and Euro IV if they don't go with urea,' he said.
A spokesman for the Environmental Protection Department and the Transport Department said vehicle owners could choose other models.
'We believe that the number of AdBlue supply points will be increased with market demand,' he said.