Fine particulate pollution is the easiest to filter, but not the only harm from urban air. Many chemicals like NOx compounds, CO, etc are not healthy.

Including increased accident risks, particulate, and chemical pollution together is a very different risk profile vs comparing all benefits vs a subset of downsides.

That said, you can filter out most particulates and there is little reason not to take this precaution.

I read somewhere that being in a car doesn’t protect against it either, so if it’s a choice between driving and biking then biking is still better.

Exercise increases the body's need for oxygen > which increases the rate you breath in air > which increases exposure over the same time frame.

Also, many cars include high quality air filtration which really does help.

But again, just buy a mask and deal with the actual problem.

I assume the study I read about used moderns cars to test.