The Ministry of Ecology and Environment said that at present, some progress has been made in-depth governance of key industries, and in order to formulate emergency emission reduction measures more scientifically and accurately, performance grading should be carried out according to the level of environmental performance of enterprises, while meeting the local demand for emergency emission reduction at the same time, formulate differential emission reduction measures. During the heavy pollution weather warning period, enterprises with advanced environmental performance can reduce or exempt emergency emission reduction measures, so as to encourage "advanced", spur "backward", and promote the high-quality development of the whole industry. Provinces (municipalities) in key areas shall, in accordance with this guide, continuously classify the performance of enterprises in key industries and implement differential management and control during periods of heavy pollution. In principle, the emission reduction measures of enterprises with the same level of performance in the same region, the same industry and the same level of performance are the same. Class A and leading enterprises may independently take emission reduction measures; grade B and below enterprises and non-leading enterprises shall not be less than the requirements of this technical guide. Various localities can also formulate more stringent emission reduction measures according to the demand for the improvement of ambient air quality; other industries that have not implemented performance grading can be established by the provincial (municipal) ecological and environmental departments to formulate unified performance classification standards and implement differential management and control.