Table 3. Turning points reached earlier studies by pollutant type.

Pollutant types	Study	Datasets	Period	Econometric techniques	Turning points
CO2 emission		173 countries	1990–2014	Error correction model	(402,125.361 US$)
CO2 emission		20 countries	1870–2014	Bivariate model	$18,955 and $89,540 (in 1990 US$)
CO2 emission		128 countries	1990–2014	cross-sectional dependence and slope homogeneity tests	Significant
CO2 emission		141 countries	1970–2014	Spatial Green Solow model	Statistically significant
CO2 emission		India	1970–2015	autoregressive distributed lag (ARDL)	USD 2937.77
Renewable energy		Pakistan	1970–2014	autoregressive distributed lag (ARDL)	Significant
CO2 emission		27 Chinese cities	2001–2005	Panel data parameter estimation	34,328 CNY and 47,669 CNY
Industrial CO2 emission		USA	1973–2015	multilevel mixed-effect	Significant
CO2 emission		China	1995–2011	Input-output analysis	Significant
Fuel energy consumption		East Asian and Pacific countries	1990–2014	Generalized Method of Moment (GMM)	$5112.65

Sources: Authors’ compiling by the literature review