. 2022 Nov 11;8(11):e11521. doi: 10.1016/j.heliyon.2022.e11521

Table 1.

Variables of EKC relationship.

Environmental indicators		Other types of indicators
Authors	Variables analysed on EKC relationship	Authors	Variables analysed on EKC relationship
[58]	(i) CO₂ emissions—GDP	[39]	Consumption of Primary Commercial Energy–GDP
	(ii) Ammonium—GDP
	(iii) Nitrous Oxide—GDP
[59]	6 Footprint components (Built, Carbon, Cropland,	[60]	Pollution Abatement Costs–Gross State Product
	Fishing, Forest, Grazing)—GDP	[61]	Income Inequality–Tourism Revenue
	Fishing, Forest, Grazing)—GDP	[62]	Load Capacity Factor—GDP
[63]	Municipal Solid Waste—GDP	[62]	Load Capacity Factor—GDP
[64]	(i) Timber output—GDP and FDI	[65]	(i) Primary Energy Consumption–GDP
[64]	(ii) Afforestation Area—GDP and FDI		(ii) Oil Consumption–GDP
[66]	(i) Territory-based CO₂ emissions—GDP		(iii) Natural Gas Consumption–GDP
	(ii) Consumption-based CO₂ emissions—GDP		(iv) Coal Consumption–GDP
	(ii) Consumption-based CO₂ emissions—GDP		(v) Hydroelectricity Consumption–GDP
[67]	(i) Sulphur Dioxide emissions- GRP	[68]	Energy Consumption–GVA
	(ii) Industrial Solid Waste–GRP	[69]	Coal Consumption–GDP
	(iii) Industrial Wastewater Discharge—GRP	[69]	Coal Consumption–GDP
[70]	Haze Pollution–GDP	[71]	(i) Renewable Energy Consumption–GDP
[72]	(i) Water Consumption—GDP		(i) Renewable Energy Consumption–GDP
	(ii) Industrial Water Consumption—GDP		(ii) Non-Renewable Energy Consumption–GDP
	(iii) Non-Industrial Water Consumption—GDP		(ii) Non-Renewable Energy Consumption–GDP
[73]	PM_2.5 emissions–GRP	[74]	(i) Domestic Material Consumption—GDP
[73]	PM_2.5 emissions–GRP	[74]	(ii) Material Footprint–GDP
[75]	(i) CO₂ emissions—GDP	[76]	Electricity Intensity–GDP
	(ii) CO₂ Intensity—GDP
	(iii) CO₂ emissions by sector—GDP
[77]	Residential CO₂ emissions–GDP	[78]	Fossil Fuel Electricity Production–GDP
[79]	Agricultural CO₂ emissions—Agricultural Economic Growth	[80]	Energy Intensity–GDP
[81]	(i) Wastewater Discharge—GDP	[82]	Final energy Consumption in Households–GDP
[81]	(ii) Wastewater Discharge—Urbanization	[82]	Final energy Consumption in Households–GDP
[83]	Chromium—GDP	[84]	Fossil fuel share in energy mix–GDP
[85]	(i) CO₂ emissions of solid—GDP	[86]	(i) Environmental Crimes–GDP and Education
	(ii) CO₂ emissions of liquid—GDP		(i) Environmental Crimes–GDP and Education
	(iii) CO₂ emissions of gaseous—GDP		(ii) Environmental Crimes–Household income and Education
	(iv) CO₂ emissions aggregate—GDP		(ii) Environmental Crimes–Household income and Education
[87]	CO₂ emissions—Remittances	[88]	Noise Pollution—GDP
[89]	(i) Environmental Degradation Index—HDI	[90]	(i) E-waste—GDP
[89]	(ii) Ecological footprint—HDI	[90]	(i) E-waste—GDP
[91]	(i) CO₂ emissions—GDP	[92]	Energy-Resource Depletion: (i) Energy Depletion—GDP (ii) Net Forest Depletion—GDP (iii) Natural Resource Depletion—GDP Climate Change: (iv) Perfluorocarbon emissions—GDP (v) PM_2.5 emissions—GDP (vi) Sulphur Hexafluoride emissions—GDP (vii) GHG emissions—GDP Health Resources: (viii) Tuberculosis—GDP (ix) Infant Deaths—GDP (x) Health Expenditures–GDP
	(ii) Sulphur Dioxide—GDP
	(iii) Volatile Organic Compounds—GDP
	(iv) Nitrogen Oxides—GDP
	(v) Carbon Monoxide—GDP
[93]	Composite Index of Environmental Performance—GDP

Notes: CO₂ denotes Carbon Dioxide; FDI denotes Foreign Direct Investment; GDP denotes Gross Domestic Product; GHG denotes Greenhouse Gases GRP denotes Gross Regional Product; GVA denotes Gross Value Added; HDI denotes Human Development Index; PM_2.5 denotes Particulate Matter (2.5 μm).