This paper studies the asset pricing implications of industrial pollution. A long‐short portfolio constructed from firms with high versus low toxic emission intensity within an industry generates an average annual return of 4.42%, which remains significant after controlling for risk factors. This pollution premium cannot be explained by existing systematic risks, investor preferences, market sentiment, political connections, or corporate governance. We propose and model a new systematic risk related to environmental policy uncertainty. We use the growth in environmental litigation penalties to measure regime change risk and find that it helps price the cross section of emission portfolios' returns.

Using patent lawsuit data from 2000 to 2014, we find that a stock portfolio consisting of alleged patent infringers (i.e., firms sued for patent infringement) provides significantly higher stock returns (between 0.48% to 0.61% per month) in the following year compared to other firms with similar characteristics. In contrast, plaintiff firms’ subsequent stock returns are not significantly different from comparable firms’ returns. We examine several possible explanations for this pattern, including pessimism-driven mispricing, exposure to unknown systematic risk, cash holdings, and financial constraints. Our evidence supports the explanation based on pessimism-driven mispricing.