Emission caps for Hong Kong's power plants could be tightened by as much as 28 per cent after 2020 when the city starts obtaining half of its power from natural gas. The proposed caps in the electricity sector for sulphur dioxide (SO2) and nitrogen oxides (NOx) could be tightened by 17 per cent and respirable suspended particles (RSP) by 16 per cent, under the fifth technical memorandum set between the city's two power companies and the government. The proposal will be discussed at a special meeting of the Legislative Council environmental affairs panel next Tuesday. Hong Kong Electric's Lamma power station will have to make emission cuts between 26 and 28 per cent compared to the previous allowances set for 2019, while CLP's three power stations will have to achieve reductions between 9 and 12 per cent. The Environmental Protection Department said the proposed caps factor in the new future fuel mix, announced in March. This would boost natural gas generation to 50 per cent in 2020, with imports of nuclear energy and projected electricity demand also in the mix. "The reduction will help improve air quality given that emissions from the electricity sector account for 47 per cent, 31 per cent and 16 per cent [SO2, NOx, RSP] respectively of the territory-wide emissions of these pollutants in 2013," according to the department. If approved, this will be the fifth time the caps have been tightened since 2010. Since then, power plant emissions have decreased by 40 to 63 per cent. Both companies considered the proposed new allowances "extremely challenging" but were committed to ensure compliance. Both said they saw compliance of the emission allowances contingent upon having the supply of fuels of the right quality. Clean Air Network's Kwong Sum-yin said the tightening of standards would be "significant", thanks to the increased use of natural gas in the fuel mix. "[However] natural gas should only be an interim option. To see a deeper cut in emissions, the government needs to consider further adoption of renewable energy," Kwong added.