| Methane | Nitrous | CO2 | Greenhouse |
Levin, Lin and Chu [25] | 0.3278 | 0.1587 | −3.989* | −2.0174* |
Harris and Tzavalis [20] | 0.9718 | 0.933 | 0.9468 | 0.9383 |
Breitung [21] | 2.6478 | −0.0376 | 2.6297 | 2.8004 |
Im, Pesaran and Shin [22] | −1.0118 | 0.5619 | −1.7418* | −1.5236 |
Maddala and Wu [19] | 48.1682 | 54.5412 | 69.0915 | 51.1836 |
Choi [24] | 43.6091 | 74.2681* | 101.79* | 82.7779* |
Hadri [23] | 87.0710 | 103.349 | 121.916 | 99.4581 |
Pesaran t-bar [13] | −1.0630 | −1.8640 | −1.7940 | −1.5460 |