Final answer:
Pollution limits can be hard to implement due to the variation in pollution sources and the rigid nature of command-and-control regulations, which include specific emissions limits and pollution-control technology requirements, yet often contain politically motivated loopholes.
Step-by-step explanation:
One reason pollution limits are difficult to implement is due to the variation in pollution sources. Command-and-control regulation, which encompasses such pollution limits, faces challenges due to its nature of setting specific limits for pollution emissions and specific pollution-control technologies. This traditional regulatory approach has helped protect the environment but presents issues such as lacking incentives for firms to reduce pollution beyond the set limits, offering limited flexibility in methods of reducing pollution, and containing loopholes that are often politically motivated. Additionally, command-and-control regulations may require companies to install costly anti-pollution equipment, making them account for the social costs of pollution in their production decisions, thereby increasing the complexity of implementation.