Introducing buses powered by natural gas and trolley buses could improve air pollution, according to a Hong Kong University study. The $1.5 million report also says the Legislative Council should be partly blamed for the environmental plight, echoing comments by environmental protection officials. "Legco sometimes seems more concerned with its own internal political agendas," say authors Dr William Barron and Dr Nils Steinbrecher in the report, titled "Heading Toward Sustainability". The study identifies diesel buses and minibuses as the two major sources of air pollutants.