The city will cap its annual coal consumption at 15 million tonnes by 2015, setting a stricter goal compared with the previous one of 20 tonnes for the same time frame, according to Beijing's development and reform commission, the city's top economic planner. Beijing also wants areas inside its 5th Ring Road to be coal-free by 2015, said Gao Xinyu, head of the commission's energy division. Over the past two years, the city has already invested 12 billion yuan (1.9 billion U.S. dollars) in replacing the coal-fired heating systems of 160,000 homes in its downtown areas. The government also offers subsidies to residents who use electricity for winter heating. Vice Mayor Hong Feng had previously said that reducing the amount of coal burned is one of the most important efforts being made to reach the city's pollution control target, as coal still dominates the city's energy mix. Beijing consumed 26.35 million tonnes of coal in 2010, accounting for 30 percent of its total energy consumption, while the other 70 percent of its energy consumption was made up of natural gas, imported electricity as well as new and renewable energies. To achieve the ambitious target, the city will replace four major coal-burning power plants with natural gas power plants, ban coal-fired winter heating and use more clean energy, said Zhao Lei, deputy director of the commission. The city's air quality has been improved over the past few years since it shut down 180 polluting and energy-consuming companies and over 200 coal mines. In the 1990s, coal accounted for over 40 percent of the city's energy consumption. Beijing in January began to disclose readings of PM2.5, fine particulate matter 2.5 micrometers or less in diameter, following public outcry about the accuracy of official air quality readings which regularly ranked pollution levels as low, even when a thick smog could be seen. The city had previously based its air quality information on readings of PM10, particulate matter 10 micrometers in diameter or larger. PM2.5 is small enough to bore deep into the lungs and even pass into the bloodstream, causing respiratory problems and other illnesses. It mainly comes from dust and the combustion of fossil fuels, and is the main component of haze. Last month, the Beijing municipal government announced that it aims to reduce the city's average PM2.5 reading from the current 70 micrograms per cubic meter of air to 50 micrograms by 2020. However, if pollution from burning coal cannot be curbed, reducing PM2.5 will be just "empty talk," said Qu Geping, former chief of the country's environmental protection bureau.It will be no easy task for the city to reach its 2015 goal, let alone become "coal-free," as it is extremely hard to banish the 2.15 million small coal furnaces in the city, said an environmental protection expert who refused to be named. The furnaces are widely used in downtown Beijing, the city's outlying areas and the countryside. They burn inferior coal, which could produce nearly one-hundred times more emissions than large coal-burning facilities, Gao Xingyu said. Meanwhile, it takes a long time and a huge investment to build more natural gas pipes and increase the gas supply, said the anonymous expert. It is possible that Beijing will still need 10 million tonnes of coal per year by 2020, he said.