The Effect of Urbanization on Air Pollution Damage
研究发现，人口向城市迁移导致城市空气污染排放的边际损害大幅上升，尽管美国总排放量下降，但1970-2000年间全国总损害反而增加，直到2000年后因氮氧化物和二氧化硫排放大幅减少才下降。
The global shift of population from rural to urban areas has dramatically increased the marginal damage of air pollution emissions in urban areas. Despite a steady decline in overall emissions in the United States, this rising marginal damage in urban areas caused total national damage to increase from 1970 to 2000. Total damage only fell after 2000 because of a dramatic decrease in nitrogen oxide and especially sulfur dioxide emissions. The rising marginal damage in urban areas suggests that environmental policy should emphasize reducing urban emissions of particulates, volatile organic compounds, ammonia, and sulfur dioxide.