sentences:  According to Reuters, in September 2013, the Chinese government published the plan to tackle air pollution problem on its official website.The main goal of the plan is to reduce coal consumption by closing polluting mills, factories, and smelters, and switching to other eco-friendly energy sources.These policies have been taking effect, and in 2015, the average PM2.5 in 74 key cities in monitoring system is 55 μg/m3, showing a 23.6% decrease as of 2013.