Fig. 7
From: Exhaust emission factors of greenhouse gases (GHGs) from European road vehicles
Effect of Euro standards on the CH4 and N2O average emissions from light-duty (top panels-a) and diesel heavy-duty (bottom panels-b) vehicles. “Hybrid” category includes hybrid-gasoline vehicles. Horizontal lines stand for the unique values from group composed of one vehicle only. Kruskal–Wallis statistical test with ns: p > 0.05, *p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001, ****p ≤ 0.0001