PM 0.3, 2.5 and 10 are the three categories of concern in urban/ traffic pollution. Depending on the rating of the mask most of this can be filtered out with a good fitting mask.
The key thing is to look for N99, P99, FFP3 / P3 ideally with 2CV afterwards. These filter out 99% of all PM 0.3 to PM 10 particulates. That's down to 0.3 microns. That's covering diesel sourced particulates that can pass into your blood.
Truth is you're unlikely to get a good fit without training and mask fitting. Totobobo seem to understand that by the way they are promoting a way to customise their masks for a better fit. Complete with a way to test its effectiveness. Iirc when correctly fitted you can see moisture build up in the clear mask. A kind of moisture tide line all around your mouth and nose area. Totobobo masks ship with N90 filters iirc. They filter only 90% of those particulates they do supply replacement filters for N95 and N99 ratings (95% and 99% of particulates).
You have to read the small print I reckon.
I did find a link about determining pollution levels. It's about distance you can see through it. No haze = no need for a mask, 1 to 2km visibility you need it and the filters probably only lasts a couple of months. Something like that anyway. More pollution the more often the filters need replacing. Totobobo are white and you replace when it's too dark. Others less clear. Some are simply based on fixed times based on hours use for different pollution levels.