The environmental Kuznets curve for US counties: A spatial econometric analysis with extensions

We examine the relationship between county per capita income and toxic pollutants using a comprehensive model of the Environmental Kuznets Curve. The model incorporates ethnic diversity, spatial effects and most independent variables used in previous studies. Initial results suggest that the relationship follows an inverted-U-shape. However, incorporation of a cubic term for income reveals that toxic pollution eventually increases again as income continues to rise. Ethnic diversity and spatial effects are found to be important in understanding toxic pollution in US counties. We also detect an EKC-type relationship with respect to income inequality.