Carbon dioxide is a ventilation proxy, not a pollutant measure
Indoor CO2 concentration indicates how much outdoor air is being delivered per occupant. It says nothing about particulate, chemical or biological contamination. Low CO2 with poor filtration is entirely possible.
Particulate counts depend on where you measure
PM2.5 at a wall-mounted sensor beside a doorway reports something different from a sensor in the occupied zone. Sensor placement, height and proximity to supply diffusers change the reading more than most facilities teams expect.
Humidity is the parameter most often neglected
Sustained low humidity affects comfort and respiratory health. Sustained high humidity risks condensation and microbial growth within the building fabric. Both are controllable and both are frequently left unmanaged outside design conditions.
Volatile organic compounds need context
Total VOC readings from low-cost sensors indicate change rather than absolute risk. A spike after cleaning or new furniture is expected. A persistent elevated baseline warrants investigation with laboratory methods rather than a dashboard reading.
