Abstract:   Lack of policy guidance in low-carbon technology innovation poses dual externalities in terms of technology and environment, which severely inhibits the vitality of enterprises in low-carbon technology innovation. To explore whether the implementation of low-carbon development and intellectual property protection policies effectively alleviates the dual externalities of low-carbon technology innovation, this study examined a sample of high-carbon emission enterprises listed on A-share markets and major cities across China from 2007 to 2021, by using the Difference-in-Differences (DID) and difference-in-differences-in-differences (DDD) methods. The findings are as follows: (1) Both the low-carbon city pilot policy and the intellectual property demonstration city policy effectively alleviate the dual externalities of low-carbon technology innovation at both the city and enterprise levels. This conclusion remains valid after addressing endogeneity and undergoing multiple robustness tests. Further heterogeneity studies revealed that these two policies have a better effect on promoting lowcarbon technology innovation in enterprises located east of the "Hu Line", non-state-owned enterprises, lightly polluting enterprises, and startups. (2) The mechanism tests indicated that low-carbon development and intellectual property protection policies alleviate the dual externalities of low-carbon technology innovation by enhancing enterprises′ environmental attention and innovation attention, respectively. (3) The results of policy interaction tests showed that there is a synergistic effect between the two policies, and the effectiveness of this synergy is greater than the individual effects of each policy. This research will deepen the understanding of enterprise competition theory in the context of low-carbon development, expand the research boundaries of externality issues in low-carbon technology innovation, explore the research ideas and methods for the synergistic effects of multiple policies, and provide theoretical references and empirical evidence for the construction and improvement of relevant policy systems in the future.

Key words: low carbon city pilot, intellectual property demonstration city, low carbon technology innovation, double externality