Urban Air Quality Benefits from China's Emerging Shale Gas Revolution: Taking Urumqi as an Example

China is seeking to unlock its shale gas in order to curb its notorious urban air pollution, but robust assessments of the impact of replacing coal for winter heating with natural gas on PM2.5 pollution are lacking. Here, using a whole-city heating energy shift opportunity offered by greatly reduction of coal combustion during the heating periods in Urumqi, we conducted a four-year study to reveal the impact of the replacement of coal by natural gas on concentrations of PM2.5 in Urumqi, northwest China. We found more than 60% decline (P<0.01) in PM2.5, major soluble ions and metal elements in PM2.5 in January of 2013 and 2014 compared with the same period of 2012 and 2011 (e.g., PM2.5 concentrations averaged 79, 120, 323, 322 µg m-3 in January of 2014, 2013, 2012 and 2011, respectively), reflecting significantly positive effects of natural gas as a whole-city heating fuel on air quality. This is because the complete replacement of natural gas for heating energy occurred in October 2012. Meanwhile, weather condition in winter did not show significant change in the past 4 years. Our results reveal that China or other fast developing nations will greatly benefit from the change of energy structure, that is, increasing natural gas or shale gas ratio in total energy consumption while reducing the coal consumption.