A worker checks a gas-fired boiler at a plant in Xi'an, capital of northwest China's Shaanxi Province, Dec. 14, 2017. Air pollution has been notably reduced in Xi'an, especially during the winter months this year. The government has taken a series of measures to fight air pollution: replacing coal with clean energy, limiting cars, reducing dust, etc.. Levels of PM10, PM2.5 and SO2 were down 33 percent, 36 percent and 17 percent respectively year-on-year from the beginning of November. (Xinhua/Shao Rui)