No building is air-tight. Even a well-sealed home has a continuous low-rate exchange of indoor and outdoor air through the building envelope, door seals, electrical penetrations, window frames, HVAC duct boots, chimney. This passive air exchange is called infiltration. The rate is driven primarily by wind and by indoor-outdoor temperature differences (the stack effect).
LBNL building-science measurements place typical North American residential infiltration at 0.2–0.5 air changes per hour (ACH) in still calm conditions, rising to 1.0+ ACH at 30 km/h winds, and 1.5–2.0 ACH or higher during storms. For comparison, the ASHRAE 62.2 minimum total ventilation rate is roughly 0.35 ACH, meaning that on a windy day, passive infiltration alone may exceed code minimum.
For interpretation: wind affects all the outdoor-cross-reference parameters Terrestream tracks. On a windy day, outdoor PM2.5, NOx, SO2, ozone, and pollen all infiltrate your home at higher rates. The dashboard reads outdoor wind speed from Open-Meteo and adjusts its outdoor-influence estimates accordingly. A wildfire-smoke day with 30 km/h winds is meaningfully worse for indoor air than the same outdoor PM2.5 level on a still day.
Practical implication: during outdoor air events (smoke, high pollen, ozone), tightening the building envelope helps, closing windows, sealing obvious gaps, switching HVAC to recirculate. During favorable outdoor air conditions, mild infiltration provides "free" ventilation that lowers indoor CO2 and VOCs without any energy cost.
References
- LBNL - Building air infiltration doi.org
- ASHRAE - Handbook of Fundamentals www.ashrae.org
- Open-Meteo - Forecast API documentation open-meteo.com
- NOAA NWS - Wind safety www.weather.gov
