环境政策促进技术变革了么：来自排放税与研发投入的证据（RFS2022）
题目：Can Environmental Policy Encourage Technical Change? Emissions Taxes and R&D Investment in Polluting Firms
摘要：Higher country taxes on noxious manufacturing emissions lead to substantial increases in firms’ R&D spending. The R&D response is entirely driven by those high-pollution firms most affected by emissions taxes. Pollution taxes increase the marginal value of R&D spending in polluting firms, even when this spending does not lead to new innovation. Pollution taxes have the strongest effect on R&D investment in sectors in which new invention is difficult to appropriate and outside knowledge is easier to acquire, suggesting an important reason dirty firms invest in R&D is to expand their capacity to absorb external knowledge and technical know-how.
研究问题：how country-level taxes on dirty manufacturing emissions affect technology spending in high-pollution firms.
研究动机：Although several studies highlight the key role technology spending plays in firms’ efforts to re-engineer production and reduce pollution at the source (e.g., Hammar and Löfgren 2010; Xie et al. 2015), there is little systematic evidence that environmental policy can encourage polluting firms to make these investments.
研究设计：After merging data from these various sources, we work with a primarysample of around 33,500 firm-years across 18 countries over the period 1990 to 2012.运用不同国家排放税强度做多时点DID，进一步做动态效应分解；利用企业所在行业的污染排放量高低作为异质性分组。
研究发现：
We document a strong positive link between taxes on SOx emissions and firminvestment in R&D.
In addition, the effects of higher SOx taxes are concentrated in firms located in more pollution-intensive industries.
These differential effects indicate causality because firms in pollution-intensive industries are more exposed to (or treated by) the higher pollution taxes (e.g., Rajan and Zingales 1998).
We find similar differential effects when we study how R&D spending affects the market value of the company’s equity;
these tests show that a marginal dollar of R&D is more valuable when polluting firms face higher emissions taxes.(还有很多其他发现)
研究贡献：
Our research contributes to the empirical literature on how innovative activity responds to environmental policies and regulations.
Our study complements Aghion et al. (2016), who show that higher taxinclusive fuel prices lead to clean energy patenting in the auto industry.
Our findings are also relevant for evaluating and modeling the macroeconomic consequences of environmental policies
Finally, our work is part of an emerging literature on the linkages between finance and the environment.
除此之外：
Moreover, as Jaffe, Newell, and Stavins (2002) discuss, market-based environmental policies (such as pollution taxes) may provide stronger incentives for firms to implement cheaper and more efficient production technologies compared to the command and control approaches (such as environmental compliance regulation) that have been studied in prior work. （市场激励型 VS 命令控制型）
The specification includes both firm and year fixed effects (ηi and ηt ). Firm fixed effects account for any unobserved, time-invariant firm characteristics that may affect R&D, including any stable characteristics of the country in which the firm operates, such as culture, institutional quality, and accounting conventions. Year fixed effects control for aggregate time-varying shocks common to all firms in all countries.（个体固定效应和时间固定效应解释）
This section develops several cross-sectional tests to distinguish the two roles of R&D investment: generating new innovation, and enhancing the firm’s ability to assimilate and exploit outside knowledge.
