Final answer:
The primary reason environmental economists are interested in externalities is to improve public health by understanding and mitigating the social costs caused by pollution and resource depletion.
Step-by-step explanation:
Environmental economists are particularly focused on externalities because these are costs or benefits arising from a production process that affects third parties who are not directly involved in the transaction. The primary reason for their interest in externalities that damage the atmosphere, water supply, natural resources, and overall quality of life is b) To improve public health. Externalities can create substantial social costs - such as pollution and resource depletion - which in turn can result in negative health impacts for the public. Environmental economists aim to understand these costs and help mitigate them through policies and regulation, ensuring that society accounts for the true cost of economic activities. Economics as a broader field is concerned with the well-being of all individuals in society, and this includes addressing externalities. By recognizing how externalities influence public health, the environment, and quality of life, environmental economists play a role in determining how to balance economic activity with environmental sustainability, thus ensuring that both present and future generations can enjoy a healthy living environment.