That helps for pollution that comes from outside (traffic, pollen, wood smoke), but most of the microplastics are generated by moving/wearing synthetic textiles inside the home.

Positive pressure systems are great, love 'em, but there's a quantitative mismatch in this case. Above ~1 ACH your HVAC costs will go through the roof (even with heat/humidity recovery), but for effective filtration you need 6-8 ACH to catch the larger dust before your lungs do.

And for pm2.5, at least in Australia, it’s entirely generated from cooking. Outside air is very clean.