Why Indoor Air Is Often Worse Than Outdoor Air

Why Indoor Levels Are Higher

Outdoor air is continuously diluted by wind and atmospheric mixing across an essentially unlimited volume. Indoor air is confined to the enclosed volume of your home with limited exchange. Every pollutant source inside the home (cooking, cleaning products, building materials, furniture, human activity, pets) adds to the concentration in that enclosed space. Unless ventilation actively replaces indoor air with outdoor air, concentrations build.

The Practical Takeaway

This is not about being afraid of your home. It is about recognizing that indoor air quality requires attention the same way water quality and food safety do. Source control (reducing what goes into the air), ventilation (exchanging stale air for fresh), and filtration (cleaning the air that stays) are the three strategies. The assessment identifies which of these needs the most attention in your specific home.