Answer:
True
Step-by-step explanation:
It's true that old vehicles like the ones found in Africa and in other poor countries contribute a lot to the air pollution.
But it's far from the only reason... it's probably not the most important reason for most countries either. The main reasons would be big factories without any air pollution control, and the total eradication of air-purifying forests.
This is mostly the doing of the industrial countries... either by colonisation or by exporting factories in places where they had lower environmental controls to attract investments.