I’m sure but is it enough to cause cancer? What other environmental toxins are we breathing in? I know that whenever I get out of my pristine rural setting to the big city I get horrible headaches, I always attributed them to the exhaust from so many cars.
About the only thing in car exhaust is water vapor and CO2. (that's why the communists invented global warming to knock us down)
In the country, there is probably a lot more Oxygen due to the trees and grass, where the city has very little.