Functional form of water pollutants-income relationship under the environmental kuznets curve framework

There have been numerous theoretical and empirical studies of an income-pollution relationship, which is usually referred to as the environmental Kuznets curve (EKC). The hypothesis underlying the EKC is that the level of environmental degradation will increase as per capita income increases up to a certain threshold. Traditionally, when the turning point in the pollution-income relationship is estimated in the EKC framework, a single equation panel data model with an assumed functional form of income is the norm. Flow pollutant is generally regressed against various functional forms of income and other variables hypothesized to contribute to pollution. Environmental Kuznets curve models have been estimated either with a quadratic or a cubic specification form between the level of pollutant concentration and per capita income. Environmental Kuznets curve models have been estimated either with a quadratic or a cubic specification form between the level of pollutant concentration and per capita income