Hong Kong power plants will have to cut their emissions of three key pollutants by up to 17 per cent, starting in 2017, the Environmental Protection Department said on Friday. In the second air-quality initiative in two days, the new emissions caps were set at 10,399 tonnes for sulphur dioxide, 25,950 tonnes for nitrogen oxides and 750 tonnes for respirable suspended particles. Those levels represent reductions of 17 per cent, six per cent and 10 per cent in the three pollutants, respectively, compared with caps that will come into place in 2015. “The tightened emission allowances will help improve the air quality in Hong Kong and the Pearl River Delta region,” the department said. Power generators accounted for between 16 and 50 per cent of the emissions of the three pollutants across the city, according to government figures. Officials will table the proposal in the Legislative Council on Wednesday. The announcement came one day after Environment Secretary Wong Kam-sing said the government may phase out old diesel-powered commercial vehicles. The new emissions limits were announced as the city recorded very high levels of air pollution in three busy districts. The pollution index at roadside stations in Central, Mong Kok and Causeway Bay reached 100 on Friday. People with heart or respiratory illnesses are warned to reduce physical exertion and outdoor activities when the reading reaches 100.