Commute exposure is well-characterized in the literature and it is not small. A driver in stop-and-go traffic breathes cabin air that accumulates NO2, ultrafine particles, and polycyclic aromatic hydrocarbons from the tailpipes of the vehicles a few meters ahead; Harvard's commute work has documented spike-to-baseline ratios of 5-10x for these pollutants compared to the same person's indoor home environment. Transit riders breathe a different mix: airborne pathogens and crowd-driven PM, with diesel exhaust contributing on bus routes. Cyclists pull deep lungfuls of cabin-exhausted air next to tailpipes at exactly the time their respiratory rate is doubled by exertion, which is the worst possible scaling for dose.
A fixed indoor sensor cannot read any of this, by physics. The Terrestream module lives at one address; the SEN66 measures the air at the sensor's location and nowhere else. Sending the device on a commute is also not a workaround: the PM intake fan and the gas sensors are not weather-sealed, the module is calibrated for indoor conditions, and the wifi backhaul disappears the moment you leave the house. The honest answer is that personal-exposure measurement is a different instrument class. WHO outdoor-air guidance exists precisely because outdoor exposure has its own monitoring infrastructure.
What does work for commute exposure: portable personal-exposure monitors (Atmotube Pro, AirVisual portable units, Plume Labs Flow) which are battery-powered, weather-tolerant, and Bluetooth-paired to a phone. Phone-app-only approximations work too: pull the nearest EPA AirNow or NAAQS reference station reading, multiply by the time you spend outdoors or in traffic, and adjust upward by 2-5x if the commute is in stop-and-go congestion. The arithmetic is rough but the order of magnitude is right, which is more than enough to inform decisions like "is biking on this corridor a good idea this week" or "should I avoid running outdoors during the afternoon rush."
What Terrestream does help with: characterizing the indoor environment you spend the rest of your day in. For most people that is 16 hours at home and 8 hours at work, which is 80% of waking exposure once you subtract sleep. Optimizing the part of exposure the device can measure is rational even if the commute remains a blind spot. The dashboard is also useful as a comparison anchor: when the indoor PM2.5 reading is 4 µg/m³ and the AirNow station reads 18 µg/m³, that gives you a sense of the gradient you walk through every morning. See outdoor air feeds for how the dashboard pulls outdoor reference data, dose and time-weighted exposure for the framework that ties commute and indoor exposures together, and accuracy and confidence for what the indoor reading does and does not generalize to.
This is general guidance, not a substitute for professional assessment of your specific home. Major interventions (HVAC redesign, sealing a leaky envelope, mold remediation, electrical work for fans or venting) should be done with a certified professional. For chronic problems that don't respond to the steps here, see when to call a pro.
References
- WHO - Ambient (outdoor) air quality and health www.who.int
- Harvard T.H. Chan - Commuting and air pollution www.hsph.harvard.edu
- EPA - NAAQS table www.epa.gov
- AirNow - AQI Basics www.airnow.gov
