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Title should be: "25 Percent of Cars Cause 90 Percent of Vehicle Air Pollution"

That's more likely to mislead, because it implies a difference between 'Car' and 'Vehicle', and 'Vehicle' can include trains, ships, planes, etc.

25 percent of Automobiles Cause 90 Percent of [Automobile] Air Pollution.

Even better.

Ok, we've changed to that. Thanks.