The key word is "particle". Of course if you don't count the kind of pollution that exhausts produce and tires don't, then tires look like they cause more pollution than exhausts.
Exhausts vastly improved, got carefully catalysed and filtered. So they actually might now pollute less. Also particulates are nastier than gases, as they locally accumulate in environment and lungs.
Ah ha! So this is in the same vein as Reagan's trees causing more pollution than cars?