Catalytic Converter

"During a cold start, the engine pushes hot combustion gases through the cold catalytic converter. The catalytic converter must gradually warm up in order to develop its chemical cleaning effect. As long as it is cold, carbon monoxide, nitrogen oxides (NOx) and unburned hydrocarbons penetrate unhindered into the outside air. The good emission values of modern Euro 6 vehicles are only achieved with a warm catalytic converter. The differences are drastic: in the first 5 minutes after a cold start, a vehicle emits more pollutants than a 1000 km, non-stop, drive with a warm engine. Petrol consumption and carbon dioxide emissions are 35% higher in the first 5 km, as a cold engine requires a "richer" fuel mix "

Cold start - catalytic converter

Because the engine is cold and thus catalytic converter is also cold. Its effectiveness will be bad. Only when the engine gasses warm up to warm up the catalytic converter will the catalytic converter become more effective