CLP Power's carbon dioxide emissions rose 8.5 per cent last year, hitting a 15-year high as it generated power for the city using more coal and less natural gas. The city's biggest power supplier also emitted a quarter more nitrogen oxide - a smog-inducing air pollutant - after reductions were achieved in the previous two years. The company blamed depleted gas reserves in Hainan for the greater reliance on coal. CLP Power did not rule out using less gas this year unless its liquefied natural gas terminal project - which the government is still studying for feasibility - was approved soon. Natural gases accounted for just 23 per cent of the company's fuel mix last year, down from the 31 per cent in 2006. Coal use increased from 40 per cent to 48 per cent, while the share of nuclear power remained at 29 per cent. Greenhouses gas emissions from the Castle Peak and Black Point power stations hit 19.5 million tonnes, the highest since 1993, and 8.5 per cent more than 2006. The increased reliance on coal saw nitrogen oxides in the air surging to 30,500 tonnes, although this was still within emission caps imposed by the Environmental Protection Department, CLP Power said. Sulfur dioxide emissions fell by 3 per cent to 35,100 tonnes last year, but the level of particulates rose by 5 per cent to 1,500 tonnes. Lo Pak-cheong, station manager of the Castle Peak Power Station, said the LNG terminal project was needed if the company was to deliver on its pledge to increase gas use to 50 per cent of the fuel mix. He said they could not import more energy from the nuclear plant in Daya Bay as the supply was capped. A department spokesman said it had urged CLP Power to find alternative gas supplies. Frances Yeung Hoi-shan, a Greenpeace energy campaigner, said the emission caps for power plants were either too lenient or tailor-made for the power operator.