CO2 emission GNE0877 means the difference between the CO2 emissions of the studied system and the reference system. For example, United Nations Framework Convention on Climate Change (UNFCCC) defines the certification emission reduction (CER) for clean development mechanism (CDM) projects, with CER equal to the CO2 emissions of baseline minus the CO2 emissions of project and leakage emissions (UNFCCC, 2013). CO2 emission reduction RCO2 can be obtained by calculating the input and output of the studied system and the reference system, as shown in Equation (2).equation(2)RCO2=CO2emissionsofthestudiedsystem-CO2emissionsofthereferencesystem
2.2. The definition, classification and survey of industrial symbiosis in ISMs in China
2.2.1. Defining symbiotic measures in ISMs
This definition makes even more sense in the context of China. It has been pointed out that most ISMs in China are still focusing on cleaner production inside the enterprise (Dong et?al., 2013, Guo and Fu, 2010 and Li et?al., 2010b), which is considered as an early stage in the development of industrial symbiosis (Dong et?al., 2013 and Harris and Pritchard, 2004). The definition also fits the country's ambition and efforts in developing a circular economy, which is high on its policy agenda. Cleaner production within an enterprise and synergistic measures between different actors are two pillars in the concept and discourse of circular economy (Yuan et al., 2006). With these concerns, relevant studies, such as the works by Dong et al. (2013) and Zhang et al. (2013), considered both of them in exploring industrial symbiosis in ISMs in China.