Competently built modern houses are well sealed, so not much air filters in through leaked walls, doors, etc. Instead, outside air is actively introduced through a filtered intake, by a fan (or by deliberate negative pressure, but that’s riskier, as air will come in through other paths too, bypassing the filter and potentially introducing contaminants from the structure and/or soil into the building).

There are plenty of systems to do this. My favorite is an ERV, with an aftermarket, oversized, upgraded supply filter.