I've seen this study before that claims that air pollution is worse for car drivers[1][2] than cyclists and pedestrians. If that's true a cargo bike is going to be a win over driving if air quality is an issue for you.
Take with a pinch of salt though, I can also see counter studies[3].
In older cars without cabin filters, it makes sense that air pollution is at least as bad inside the car as it is outside, it is, after all, the same air.
But modern cars usually have cabin filters, which, if good enough, well maintained, and leak-free, should result in a significant improvement. I know Tesla made it a marketing point for the Model X, but I believe all cars built in the last decade or two have at least some kind of filtration.
On top of this you can close the circulation in cars. Something I often do and something that is not possible when cycling. I can choose routes that don't pass major city intersections but if that is not the case then it is clear disadvantage for cyclists. Electric cars will tremendously improve the situation and make more routes viable for cyclists.
But modern cars usually have cabin filters, which, if good enough, well maintained, and leak-free, should result in a significant improvement. I know Tesla made it a marketing point for the Model X, but I believe all cars built in the last decade or two have at least some kind of filtration.