An issue I've found is outdoor air ventilation vs. air filtration vs. humidity management is a tricky thing to balance overall when you don't have a central HVAC system with an ERV installed, especially when you live near a busy road or have allergy issues. If you add a CO2 monitor to your air monitoring, you'll start to see where this becomes a hard thing to balance without a large ERV or other specialized ventilation systems.
On top of that, living near a highway might not show issues on your PM2.5 / PM10 monitor, but it still shows in health statistics according to studies.