## 5 Conclusions and Policy Implications
Based on the relevant research results of this study, the related policy recommendations are as follows:  
1. Establish a reasonable initial carbon quota allocation and ETS. The conclusion of the PSM-DID model shows that ETS has indeed achieved economic and environmental benefits in China's carbon trading pilot provinces and cities, that is, the \"Porter effect\" has been achieved, but a sound and clear carbon trading allocation mechanism is required as a prerequisite. The \"Porter effect\" of the ETS policy is based on the fact that it can encourage enterprises to independently develop energy-conversation and emissions-reduction technologies and increase the added value of their products. Advanced enterprises can trade surplus carbon quotas to make up for their \"innovation cost\" and realize \"environmental welfare\" and \"economic welfare.\" Therefore, it is an essential system guarantee to reasonably allocate carbon quotas and set effective carbon price ranges based on accurate historical emissions statistics and the green technology investment of various enterprises. 2. The results of the DDD model in this paper indicate that differences in economic development and industrial development will affect the carbon emissions reduction effect of ETS. Due to the economic development and industrial development differences, such as those in the industry, service and construction in different regions and enterprises, the national ETS can achieve a successful connection and smooth transition with regions only by sticking to the unified nationwide operations and management, increasing trade transparency, formulating a strict supervision mechanism, and seeking a balance between equity and efficiency
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