1. Oliver, J. G. J., Janssens-Maenhout, G., Muntean, M. & Peters, J. A. H. W. Trends in Global CO2 Emissions: 2013 Report (PBL Netherlands Environmental Assessment Agency and European Commission Joint Research Centre, 2013).
2. WHO Air Quality Guidelines;
http://go.nature.com/3u5AIV
3. Analysis of data from Ministry of Environmental Protection;
http://go.nature.com/ryXvdv
4. State Council Executive Committee Statement (Ministry of Environmental Pollution, 13 February 2014);
http://go.nature.com/tOZNxU
5. Air Pollution Prevention and Control Action Plan State Council Document Number 37 [in Chinese] (Central Government of the People's Republic of China, 12 September 2013);
www.gov.cn