「干货」A-level经济学：负外部性 Negative Externalities

The red triangle is the area of deadweight welfare loss. It indicates the area of overconsumption (where SMC is greater than PMC) 红色三角形是致命福利损失的区域。它表示过度消费的区域（SMC大于PMC的地方）

This occurs when consuming a good causes a harmful effect to a third party. In this case, the social benefit is less than the private benefit. 当消费一种商品对第三方造成有害影响时，就会出现这种情况。在这种情况下，社会利益小于私人利益。

Diagram of negative externality in consumption 消费中的负外部性图示

If goods or services have negative externalities, then we will get market failure. This is because individuals fail to take into account the costs to other people. 如果商品或服务具有负外部性，那么我们将得到市场失灵。这是因为个人没有考虑到其他人的成本。

To achieve a more socially efficient outcome, the government could try to tax the good with negative externalities. This means that consumers pay close to the full social cost. 为了达到一个更有效的社会结果，政府可以尝试对具有负外部性的商品征税。这意味着消费者支付接近全部的社会成本。

Arthur Pigou 1920 introduced the concept of externalities in The Economics of Welfare. Pigou used the example of alcohol having external costs, such as creating more demand for police and health care. Arthur Pigou 1920年在《福利经济学》中提出了外部性的概念。皮古用酒精具有外部成本的例子，如对警察和卫生保健产生更多需求。

In 1975 William Baumol and W. Oates provided a comprehensive review of the literature on externalities in Theory of Environmental Policy. In particular, they applied economic concepts of externalities to the emerging issue of environmental costs. For example, in 1975, they mentioned some of the environmental costs which were considered to be pressing. 1975年，William Baumol和W. Oates在《环境政策理论》中对关于外部性的文献进行了全面的回顾。特别是，他们将外部性的经济概念应用于新出现的环境成本问题。例如，在1975年，他们提到了一些被认为是紧迫的环境成本。

a. Disposal of toxic wastes, 有毒废物的处理

b. Sulfur dioxide, particulates, and other contaminants of the atmosphere, 二氧化硫、颗粒物和大气的其他污染物

c. Various degradable and nondegradable wastes that pollute the world’s waterways, 污染世界水路的各种可降解和不可降解的废物

d. Pesticides, which, through various routes, become imbedded in food products, 杀虫剂，通过各种途径，浸泡在食品中

e. Deterioration of neighborhoods into slums, 社区恶化为贫民窟

f. Congestion along urban highways, 城市公路沿线的拥堵

g. High noise levels in metropolitan areas 大都市地区的高噪音水平